It’s been 9 months now and over that period of time and I’ve learnt a lot about running a goldfish tank using Walstad. Unfortunately due to relocating overseas I will shortly have to tear down my tank and put it into storage.

Today I’m going to share my conclusions as I come to an end with my Walstad tank so that anyone looking to set an aquarium up using Walstad can benefit from my experience, mistakes and observations.

Water Quality

Water quality for me has never really been an issue when using the Walstad method. When I initially set my aquarium alongside my Fluval 305 canister filter I did have a slight ammonia blip but this was quickly utilised by the filter bacteria and plants.

Running the tank without a filter for the past two months or so I’ve yet to have any ammonia show up in my tests. Having said that I think the reason for this might be that the plants were fairly well established when I disconnected the filter, as opposed to when I initially set up the tank back in February.

One thing that has been an ongoing problem and is one of the things I’d like to experiment with over time is algae in the water. When I disconnected the filter it wasn’t long before I started to notice a green tint in the water. For the most part the tint was remained slight but then after going on holidays for a week when I came back and the water algae had truly taken over.

This is what prompted me to start again with fresh soil and gravel and run the tank without a canister filter from the beginning. Currently I still have green algae water in the tank but without a filter I was expecting this due to the initial abundance of nutrients leeched from the soil.

Due to already having fish I haven’t been able to do so, but what I’d like to do (and will do if I set up a tank in the future) is to run a soil based aquarium without any fish for a month or so and see what happens with the water quality.

Alternatively with fish I guess you could just do water changes say once a week but this probably isn’t a good idea as the idea behind Walstad is to keep the water stable and let a natural ecosystem occur.

However a month of weekly water changes (60-80%) just to see if the green algae water subsides would be interesting.

I believe it is possible to balance out the large amounts of nutrients that goldfish deposit into the tank but as with anything in an aquarium it takes time to play around and see what works and doesn’t work. Not only should you only change one thing at a time but then to truly see the effect of what you changed can take anywhere up to a month itself.

One final interesting observation is that when running a filter alongside the tank, I had eventual black beard algae problems inside the tank. Upon disconnecting the filter the algae growing on the substrate, plants, aquarium glass and wood ornaments eventually died off and I was left with just the water algae.

I’m not exactly sure of the reason to this but I’d assume it’s something to do with the water algae having a preference to ammonia and the surface algae favouring nitrates from the filter.

In any case it’s never been so bad that I can’t see the back of the tank so I haven’t worried about it too much.

To use a filter or not?

There are two major factors in my personal experience that should come into consideration when deciding whether to run a filter or not with a Walstad tank.


Ammonia as a food source or nitrates?

With an adequate filter attached to an aquarium I found that the filter bacteria were easily able to outcompete plants for ammonia consumption. This was evidenced by the production of Nitrates in the aquarium as plants don’t produce Nitrates when they consume ammonia.

Whilst the bacteria held off any water algae from developing (I never had a problem with clear water when using a filter) I found that surface algae was then able to outcompete plants for nutrients and flourish.

Part of the problem here I think was that instead of 100% of the waste getting broken down in the soil and replenishing the substrate most of it was getting mechanically trapped in the filter and being broken down there.

On top of this when I did my monthly filter cleanout, I’d then lose alot of the decomposing waste when I cleaned the sponges. Over time I believe this starved the soil substrate of micro nutrients and this is most likely what caused the surface algae to thrive.

When I disconnected the filter and started again with fresh soil and gravel I was hit with green water algae whilst nearly all of the surface algae died off and vanished.

Between the two scenarios it’s much, much easier to deal with algae suspended in the water. If I had another 12 months or so to play around with my tank I’m convinced that the green algae in the water would eventually consume the initial excess burst and start to die off.

Also as the plants propagated and take off again this would also squeeze out the algae water, but again time is needed to observe this in action.


Water current

One of the unavoidable aspects of having a filter attached to a Wastad aquarium is water current. The positives of which are an even distribution of water temperature and oxygenation of the water as it passes through the filter.

Unfortunately I’ve found that in the case of a Walstad aquarium, the negatives outweigh these positives.

Temperature wise I keep a heater on the left rear wall of my tank and have it set to 22deg. My tank has coverglass and a wooden canopy so I hardly ever see the heater light come on. I also have a thermometer way over on the otherside of the tank and have never seen it drop below 22 degrees, even throughout winter.

Whilst I’m not saying coldspots might not happen, I’ve yet to see evidence of it being a problem without water current. Perhaps if you live somewhere really cold it might be more of an issue.

The other major problem with current is losing carbon dioxide. Invariably when you move water around you lose any excess as the level in the water tries to reach equilibrium with the air outside. In a Walstad tank there is no artificial carbon dioxide so you need to retain as much as you can. Having a filter push water around everywhere I feel is counter productive to this.

Whether I was running a filter or not, I’ve never had any problems with oxygenation of the water. To date I’ve never seen any of my fish gasping at the surface.

The final effect of water current I noticed when I was using the filter was the build up of debris in certain hotspots. As the plants establish themselves they become debris traps and what happens over time is you get mounds of debris appearing at the base of plants that grow densely together. I found this to be particularly noticeable with my corkscrew vallisneria bunches.

As the debris winds up being concentrated in certain spots (if it isn’t sucked up by the filter intake) you potentially wind up ‘starving’ certain areas of the substrate which isn’t a good idea.

Whether this is drastically detrimental to the theory of a Walstad tank I don’t know but the levels of trapped debris certainly were noticeable. Now without a filter I find that the decomposing debris is much more evenly spread and this in theory I’d imagine would be much better for the replenishment of the soil substrate.

Fish health

Since starting my Walstad tank I’ve lost three goldfish. One had a pre-existing swim bladder problem, one died due to a fungus infection (which occurred while I was away on holiday) and the other of pinecone disease shortly after being added to the tank (which I think was thus a pre-existing condition).

Using a proper 30 day quarantine tank before adding fish to the tank I haven’t experienced any other disease outbreaks in my tank. The remaining fish seem to have thrived and haven’t shown any signs of illness.

When starting the tank I was initially worried about an ammonia cycle but thankfully this hasn’t been a problem. I do however run a 255 litre (66 gallon) tank though so this might be a result of the large water volume, obviously if you run a smaller aquarium you have less of an error threshold.

On these results I’d say fish health problems aren’t really in issue in a Walstad tank (despite the decomposing matter along the substrate), unless you introduce new diseased fish from a fish shop without proper quarantine.

Plant health and selection

I’ve tried a fair few plants in my Walstad tank and feel I can safely say that you can forget about using any ornamental plants. Whichever plants you use need to be rugged and easy growers, moreso if you’re keeping goldfish with them.

This pretty much leaves the cheap common plants for you to stock your aquarium with.

For me this isn’t a problem but as I just love to see green in my tank to contrast the goldfish and love the natural jungle look. If you’re wanting to aquascape at all and/or try growing some of the more difficult plants you might want to instead go down the injected carbon dioxide route.

The plants I’ve had success with are Corkscrew Vallisneria, Amazon Swords, Chain swords, Crypts (great root systems to oxygenate the substrate), Java ferns, Hornwort and to a limited extent dwarf Anubias (algae loves this plant).

I did have initial success with Wisteria but I think after the initial excess nutrients were used up it had problems surviving due to a limited root system.

I’ve found that stem plants don’t seem to like the Walstad and tank and that your best bet are plants that have some sort of root system. I’ve found, and this is probably due to goldfish producing a lot of waste, that fast growers are essential.

When I turned off my filter I stocked the tank with hornwort, which I originally planted but now let float around so at to better utilise the light. I’ve found hornwort to be a great indicator of nutrients.

If there are excess it grows ridiculously fast and then slows down as things balance out. It does need to be continually trimmed though due to it’s growth speed but this doesn’t take long. If you keep it floating you also don’t have to worry about it being pulled out and disturbing the substrate.

At the moment I am trying to carpet the substrate with some hairgrass. It is growing but it’s extremely slow. I don’t know if it will eventually pickup and take off but for now (2-3 weeks) not much is happening.

Again I’d love to see how it goes over 6 months but due to time constraints that won’t be possible. The goldfish seem to leave it alone though so I imagine if given the time it would eventually cover the substrate.

Lighting

Initially I ran 3x55w T5HO tubes which wound up being 2.5WPG of light and was probably too much for my tank (hence the surface algae). Currently I run only 2 of the tubes and have them quite spaced apart (I have 1.5ft wide tank as opposed to the standard 1ft) which comes in at 1.6wpg and seems to be much more suitable.

Note that my aquarium doesn’t see any sunlight, if you have sunlight available you can probably get by with even less light.

The light system is on for 12 hours a day 10am-10pm and run on a timer. This seems to keep the plants happy so I’d say is a good starting point. If I had the time I wouldn’t mind running the tank for a month at 8 hours to see if this had any effect on the algae water (after I’d waited sufficient time to see if the algae died out on its own).

Conclusions

My experience shows that a Walstad tank can be done with goldfish and for someone thinking about it I’d highly recommend it. If for nothing then to gain a better appreciation of water chemistry and the various relationships between the different components of your fish tank.

I keep fancy goldfish though and for someone keeping single tails (comets), unless you’re particularly lucky with fish that don’t eat plants I’d probably give Walstad a miss.

If I ever to get back into the hobby (I’m sure I will) I plan to pick it up where I left off and further experiment with goldfish and Walstad in an effort to perfect it. There’s still a fair few things I’m interested in trying but for now they’ll have to wait.

In any case hopefully my experiences with Goldfish and the Walstad method are thus far enough to be of benefit to anyone looking at starting their own tank up. At the end of the day there’s nothing quite as rewarding as kicking back and observing a well stocked, plant flourishing aquarium.

For a complete rundown (including running journal of my tank) of my Walstad articles, it might be of interest to checkout my Walstad topic index page.

The last time I was away I came back and Tiger had a white patch of fuzz on her and died shortly afterwards. This time when I came back I was greeted with a lovely tank full of green algae water.

I decided this would be a great opportunity to do some replanting and re-arranging inside the tank.

First I got rid of the amazon sword in the tank and replaced it with my largest crypt. Even in a 4ft tank the sword was simply just too big and whilst the crypt was almost as large, grows much more compact then the sword which liked to spread out and completely take over the center foreground.

I also thinned out the other crypts which due to their size were crowding eachother out. I was very happy with the corkscrew vallisneria at the rear right so I pulled out the plants I had growing on the rear left and after dividing up the vallisneria I had, spread it out on either side.

Corkscrew vallisneria grows quite densely and after seeing what happens when the plants take off and how much room they can potentially take up I’d rather have thin plants then the bushy ones so that the fish have more room to swim.

I also rearranged some of the java ferns on the driftwood centerpiece and spread them out a bit, they’ve got a much better shot at completely covering it now. After doing all this and despite a 100% water change, within days the green water came back as strong as ever.

At this point I’m not sure what was causing it. As far as I could tell green water happened when there was excess nutrients or a nutrient imbalance, which made no sense seeing as nobody fed the fish while I was away. I’d have thought a Walstad tank setup for 5-6 months would be capable of producing enough ammonia on its own to keep the plants going for 5 days, apparently not.

When I rearranged the tank and refilled it I’m also not sure as to what brought the green water back so quickly.

In any case I decided that another water change wasn’t going to do much so I started a course of treatment known as the ‘blackout method’. I’ll write a more detailed article on it in the future but the gist of it is you completely cover the tank for a few days and this light starvation clears the water.

When I completed the treatment the water was still a bit cloudy, but looking much better.

That was about a week ago now and I’ve watched the water seems to be slowly heading back to green again. I’ve since also thinned out the floating hornwort I’ve got in there to promote new growth and compete with the water algae. Here’s what it looks like this morning:

This time I’d probably leave it for a month and see if whatever the green alagae water is feasting on runs out (it can’t all be ammonia as I’m getting plant growth and no new algae growth on the glass or plants). Replacing the water seems to have hurt the hornwort somewhat in that it’s gone yellow while it adapts to the new water.

At this stage I’d love to experiment some more with the walstad method and goldfish but my time is running out. I plan to move overseas by the end of November and sadly I think at this stage I’m going to be surrendering the goldfish to an aquarium and tearing down the tank.

I didn’t have any green algae water problems with a canister filter running in the tank but I have a feeling the cannister filter starved the plants somewhat and was counter productive to having soil in there which is supposed to do the filtering job. What I’d like to see is if a small internal filter placed near the top of the water so as to trap as little as possible of the mulm on the gravel, would have any effect.

I’m most likely just going to leave the tank now until I’m ready to leave and see if the water clears up on its own and how the plants react, just as an experiment so if I ever get back into it at a later stage I know whether waiting or not is going to achieve anything.

While I’m overseas I might set up a tank once I’ve got my accommodation somewhat stable but it won’t be anywhere near as big as the tank I’ve got now. I’d also probably stock it with tropical fish seeing as without further investigation I’m not entirely sure a 100% filterless Walstad tank with goldfish is possible to maintain.

The good news is my tank is going into storage here so when I do make my way back I can always get back into it. Unless anything amazing happens over the next month and a half this will most likely be my last entry into my Walstad tank journal for a while.

Thanks for reading and hopefully my experiences help anyone else out there who’s willing to try the Walstad method with goldfish in the future.

I’m happy to report that thus far this has been a success. I had a mild ammonia blip but that settled down pretty fast.

Currently the tank has a slight ammonia reading (the test kit isn’t completely yellow but isn’t green enough to register on the test card) with 0 nitrites or nitrates.

Here’s what we looked like at the end of September:

As you can see the new plants I added from Livefish on the rear left have really taken off. Out of the new plants I added I’ve found Hornwort to be the most dominant and fast growing.

Given my aquarium is a goldfish tank and is now running filterless I’ve decided to work on propagating the Hornwort to the rear left of the tank to balance out that last bit of excess ammonia.

The other plants I got were growing but none came close to the Hornwort which has flourished and the goldfish do not touch it.

I gave the tank a trim, removed all the plants in the rear left, trimmed and replanted the Hornwort along with the giant grassy looking plant which seems to do ok.

It’s kind of looking a bit bare at the moment but it shouldn’t take too long for the Hornwort to colonise the rear left. That growth you see in the first photo came from just 3 small bunches of the stuff so I can’t wait to see what happens over the next month with all the trimmings I planted.

Algae is slowly receding but is still generally making the tank look ‘dirty’. The plants are pushing out new leaves and discarding the old ones. I’m really tempted to just get in there and remove all the algae leaves with my clippers but I’ve decided to just let nature take its course.

As the plant leaves are discarded they break down into nutrients so best I not disturb the ecosystem in there, the algae leaves also give the bristle noses something to much on too.

I’ve also decided to be less aggressive with the Corkscrew Vallisneria pruning so I’m going to let it grow nuts. I really liked the shade the overgrown hornwort provided on the rear right prior to pruning so I’d like to emulate that on the right side as well.

This should protect the slower growing plants in the foreground from algae and further slow it down due to reduced light availability.

All in all I’m glad I’ve gone filterless as it seems to be working and balanced. My only regret at this stage is not going filterless to begin with. I imagine it’s going to take months before my tank fully balances itself out and the plants become truly dominant.

Ah well, considering I’m keeping goldfish I guess I should be happy with the fact that things are coming along nicely and let’s face it – could have been much worse. I’ll post another update in a month.

Here’s what the tank looked like early July:

As you can see the plant at the front, which I believe came as a hitchhiker with some other plants has grown completely out of control and is not a suitable for the foreground. I also started to notice my stem plants, particularly the ludwigia in the corner and to a lesser extent the wisteria in the middle had started to become ‘leggy’ (ie. they were turning into leafless stalks with a bit of growth at the top).

Algae also gradually seemed to get worse and I even had a mini bloom out of noweher of the green variety mid July which I wasn’t too happy about.

I started to think about why this was happening and I’ve reasoned that with the canister filter running, the canister bio bacteria were probably out competing the plants for ammonia and nitrite. Then the nitrate was being consumed by the algae faster then the plants could absorb it.

I didn’t have any fast growers in there so I ordered some plants from livefish.com.au and have now have planted them amongst the established plants in there. I’m going to play survival of the fittest and keep whichever ones dominate.

To combat the nutrient problem I’ve decided to cut out the bio bacteria altogether.

Yes you read that right, I plan to run my goldfish tank without a filter.

Anyone who has kept goldfish will tell you they are masters of water pollution so I’ve set myself up for a nervous few weeks of water testing ahead while I ascertain whether the tank is up to it or not.

I’m also a little concerned about how the carbonate hardness of the water will hold up but with a drastic reduce in the bacteria biofilter eating up kh hopefully it stays high. The soil is mixed with crushed oyster shell although with little water movement down there I doubt it will do much.

If all goes well the bulk of the ammonia produced will go to the plants (a little will be processed by the tank bacteria) as well as any nitrite produced. Plants prefer ammonia and nitrite over nitrate so they should hopefully have no problem out competing algae for it.

Currently I’m also running it without a powerhead to see how that goes. So far I haven’t had any oxygen issues, I’ve increased the lighting duration back to 12 hours and have gone back to my starting watts per gallon of 2.4 (up from 10 hours of light and 1.6wpg over the last 2 months).

My next update will be at the end of August with hopefully good news.

Finally, since my last update I’m sad to report that Patch passed away. Swimbladder must have got him in the end. He was eating and behaving normally till he died so at least he was somewhat comfortable.

I also lost the big black unnamed fish I got due to dropsy. The onset of this was drastically sudden, I remember noticing his scales pineconing one evening at feeding time and over the next five or so days he lost his black colouring for silver/white. After he started floating near the top I figured it was time to put him out of his misery.

I’m assuming the sudden loss of color to white had something perhaps to do with internal organ failure. Why this happened I have no idea but it was painful to watch.

If the tank goes well over the next month I’ll look at replacing them sometime in September which will nicely co-incide with the goldfish breeding season! Anyway, here’s a snapshot of the tank as it is at the start of August (note the slightly cloudy water as the in-tank bacteria adjust to life without a filter colony):

There hasn’t been much of a change this past month in the tank. I’m putting that down to nutrient output being balanced with plant uptake for most of the month, at least as far as Nitrates go.

I did a water test yesterday and got a reading of <5 Nitrates, 7.6ph and 12deg of kh which I'm happy with.

Now that the plants have settled my focus is on the algae that has colonised the tank in dribs and drabs. I've got green algae attacking the plants and black beard algae in random patches on the gravel bed.

A week or so back I took out one of the t5 55w HO tubes from the twin reflector that I use at the back of the tank, this dropped my watts per gallon from 2.5 down to 1.6 which I'm hoping is enough to keep everything happy and lower my algae a bit.

I did have a sad start to the month losing Tiger. I went on holiday for four days and when I came back she had a small white fungus spot on her.


All of the other fish were fine so I took her out and placed her in a hospital tank for a week treating her with quick cure. At the end of the week the week the fungus was all gone so I put her back into the main tank.

She was fine for 3 days and then began to bottom sit and was dead within 24 hours. Given that the fungus cleared and didn’t come back I’m assuming the recovery was too much for her or something else might have been happening internally.

It was slightly depressing seeing as I’d had her for a while now and she was the biggest goldfish I had with the longest tail. She’s been perfectly healthy since I got her and then goes and gets sick as soon as I go on holidays.

I’ll miss watching her eat my plants.

Patch has also developed a bit of what I think is swim bladder disease (ie. it’s not working). He’s always been an extremely weak swimmer since I got him and he balances a lot on his head. Now he can’t seem to control his floating properly and spends most of his time near the gravel where he can balance himself better.

He’s eating fine and still swims about so I’m not too concerned at this stage.

I got two new goldfish mid May and had them sitting in quarantine. I have just recently added them to the tank and they seem to bet getting along with everyone. A jet black moor and a orange/white oranda. I’ve wanted an oranda for a while now and couldn’t resist this one’s big mouth.

I also got two albino bristlenose plecos to help the other two brown ones in the tank eat away some of the algae.

I won’t be doing any pruning on the tank this month, here’s what it looks like currently:

...time for a prune!


Pruning plants is a necessity in the Walstad tank but the need to prune does decrease in frequency as time goes on. Initially a Walstad tank contains an abundance of nutrients in the water. This happens primarily because plants take a while to establish themselves and match their rate of growth to the level of nutrients being produced in the tank.

The combination of excess nutrients being leeched from the soil, the decomposition of organic matter in the tank and plants having not established themselves will usually translate into a Nitrate spike early on in the tank’s life. I was reading 20 Nitrates by day 12 despite vigorous  plant growth and from memory it peaked about 2 weeks later at 30 or so, after which it slowly began to drop till I was reading less then 10 a month after setting up the tank.

In these early stages it is important to prune your plants to encourage new growth to continue to soak up excess nutrients. If you don’t prune, plants can hit roadblocks space wise and with excess nutrients in the water this is when algae can take over and bloom.

When pruning your plants in the early stages it is important to be ruthless. Think of plant pruning as taking a number 1 clipper to someone’s dreadlocks.

The photo on the right illustrates just how much plant matter I removed earlier this month. To give you an idea on just how much you can prune, the glass on the right is 2 foot long by 3/4 foot wide. As you can see I had no reservations about just how much plant matter I wanted out of the tank.

Don’t worry if your tank looks a little bare afterwards, that’s kind of the idea. Over time your plants will grow back and before long it will be time to prune again.

Here’s what my tank looked like after the pruning session, for comparison the photo at the beggining of this entry shows what it looked like pre-pruning.


To prune your tank all you need is a sturdy hand and a sharp pair of scissors. I suggest keeping a set of scissors specifically for pruning your fish tank to avoid possible contamination. I don’t suggest gardening clippers as usually the plants we are pruning inside the tank require fine trimming and a curved clippers can be bulky to use.

For stem plants I recommend pruning them so that there’s still plenty of leaves left on the original stem. If you wish to propagate the plant you can replant the trimmed stems as I have done with some of my Ludwigia plants in the left background.

Plants with singular leaves, such as the Corkscrew Vallisneria (rear right) can be trimmed about an inch or more below the water level. They look best I find when trimmed at a diagonal as you still get somewhat of a natural look.

Bushy plants like the green Wisteria (centre/right rear) can be trimmed slowly bit by bit from the outer areas until you are happy with how it looks. I tend to trim mine so that it looks like treetops.

I wouldn’t bother trimming foreground plants unless you are trying to propagate them.You shouldn’t really have any tall growing plants in the foreground unless you are aiming for a specific aquascape design.

Over time as the excess nutrient level is balanced and your plants adjust to the output of nutrients your tank produces you will find vigorous plant growth will ease and pruning times will become less frequent. I had to prune every few weeks initially but now I am probably looking at 2 months or so between prunings.

Pruning isn’t the most fun job in the world but it is nice to have that ‘clean’ tank feeling again and it does have the tank environment benefit of deterring algae. I spend a good 20-30 minutes pruning usually and can only imagine how much time those enthusiasts with co2 powered aquascaped tanks must spend grooming their tanks.

Anyway try to enjoy it and afterwards make sure you sit back and take some time to visually appreciate your efforts! Your fish will also thank you for the extra bit of swimming space.

Algae is on the slow retreat, the front glass used to get green film over it in just a few days now it’s about 3 weeks and it’s due for a wipe. Hopefully this gets longer and longer as the plants out compete it for nutrients.

All the water parameters are looking fine, Nitrate is practically 0 which means new algae growth should be extremely slow to non-existant. I can’t wait for the black algae on my Anubias nano to die off, I haven’t seen some of those green leaves in ages!

The green wisteria continues to assert it’s dominance over the left side of the tank and attempts to choke out the red ludwigia. Sometime over the next few days I plan to do a mass prune again, I’ll take a photo and add it when I’m done.

The goldfish are going great, I did lose one zebra danio due to old age I think but everyone else is doing fine.

Here’s what the tank looked like in early April;


and here’s what it looks like now, pre pruning:

Nitrate: about 7 (goal is <10 so this is good!)

KH: 12 (quite high but won't do anyone any harm and no chance of a ph crash)

ph: 7.8 (usually at 7.6 but i'm assuming has crept up slowly due to the kh settling so high. I have 0 kh out of my tap water).

I decided to do some pruning today because the wisteria was going nuts and suffocating anything near it of light and space. Here's what it looked like before:


I don’t have much experience with pruning so it looks a but ugly at the moment with the stem roots exposed but it will grow back nicely. At least I can see my java fern again! Here’s the final product.


As you can see the ludwigia at the rear left has completely straightened up and is growing tall, the vals on the rear right are coming along nicely and the sword in the middle is shooting up some nice healthy new leaves to replace the sad looking old ones.

When I initially set up my tank I used pea sized gravel on its own for the substrate and while some of plants did grow I found after a few months the dissolved oragnics in the water would stain the water yellow and the plants weren’t doing as well as they could have been.

The dissolved organics were obviously coming from the gravel substrate, to remedy this I began an aggressive gravel vaccuum routine and added fine polyfilter media to my cannister filter to catch tiny particles that would normal wind up in the gravel bed.

This worked but the poly pads would slow the filter water flow down in just one week. So much so that they were ridiculously hard to clean and I just wound up replacing them from week to week.

There had to be an easier way to maintain a tank; the Walstad method.

The basic priniciples of a Walstad tank are;



• A two layer substrate, about an an inch of soil mixed with crushed oyster shell or coral then covered by an inch or so of gravel.

• Moderate lighting, anywhere from 1.5 to 2.5 watts per gallon or 0.4 to 0.7 watts per litre. Some people use less and utilise sunlight. I don’t advise this for algae reasons, but appreciate that it works for some people algae free.

• The concept of a complete bio-ecology. You feed the fish who feed the soil substrate which feeds the plants along with light which provides oxygen to the tank and controls nutrients along with nitrate levels.


This sounded ideal in principle but I wasn’t confident in tearing down my 66g (255L) tank just yet, so I thought I’d try it on my betta tank first.

I bought a 5kg bag of potting mix soil from Bunnings (about $2.50-$3) and yanked two bunches of vallisineria from my 66g and set it up. Setting up a small Walstad tank took less then an hour and the results were fantastic.

In about a month my two bunches have propoagated into six and are all growing nicely. I don’t do any water changes on this tank, I just top up due to evaporation adding a few drops of Prime water conditioner (0.375mls of Prime will treat 15L) every so often and add a pinch of bicarbonate soda to help buffer the water as I have very soft tap water.

I’ve had a bit of brown algae (diatoms most likely) form on the glass, but haven’t had any algae problems in the tank itself, other then a bit of algae on the original bunches pulled from the 66g which will hopefully eventually die off.

Ammonia and Nitrite have read 0 since day 1 and the tank is nice to look at. Ideally I would have added a lot more plants to begin with, maybe some crypts and a hygro for some variety but with excess nutrients seeming to not be a problem and the prospect of a jungle of val appealing to me I left it as it was.

Happy with seeing how the Walstad idea work in my betta tank last week I decided to apply the method to my main goldfish tank.

I used 20kg of potting soil from Bunnings again ($5) and decided to go with a darker substrate as I’d had enough of white. My reasoning was if I did have an algae breakout, a darker substrate was nicer to look at, a white substrate caused a fair bit of glare fom the lights reflecitng back into the tank washing out colors and I’d read that fish were more comfortable with a darker substrate.

I picked up a bag of 20kg ‘midnight black’ gravel from Aquarium Supermarket (he doesn’t advertise them online but he has them in his storefront) for under $20. I had a 2kg left over bag of crushed oyster shell from putting some in my filter. If your local aquarium doesn’t stock crushed coral or oyster shell I got mine from a petstore in the Bird section for about $5, apparently it’s useful for chickens too.

Day 1: 20th February, 2009

During the tear down the fish were housed in my quarantine tank. My quarantine tank is a 60L plastic storage tub from Bunnings that was about $10, when using it as a quarantine tank I use a Fluval 2+ internal filter to keep the water clean.

After the tank was empty the first step was to add the soil. I emptied the 20L bag into the tank and spread it out evenly. I found 20L of soil was perfect for about an inch depth in a 255L.


I then added the crushed oyster shell and mixed it in through the soil. 2kg was plenty enough for 20L of soil so 300-400g per 5L of soil should be enough. Next came the gravel layer around the edge. This is done I believe to settle the the soil on the edges so you can work with the centre.


After the outer ring of gravel is placed you can start placing the plants in the soil and then covering a circle around them with gravel.

If you were like me and had driftwood you wanted to place before the plants, put in the rest of the gravel and spread it out. Place your driftwood first and then add the plants carefully by moving the gravel aside where you want the plant to go so that the soil is exposed. Place the plant into the soil and replace the gravel around the plant.

After all the plants are in place a bowl or plate so as to not disturb the gravel and start filling up the tank.


After the tank has a few inches of water in it I had a check to see how the water looked. To my dismay it was cloudy.


I’d used the same brand of soil for my betta tank and had no cloudyness problems, so I put the cloudyness down to the gravel. Even though I’d prewashed it in mesh bags in my bathtub, I find you can still often get a bit of cloudiness with new gravel.

I continued to fill the tank. My plan with the plants is to have the red ludwigia spread out and take over the back left corner, have a val jungle on the right rear corner, continue the growth of anubias nana and java fern on the two pieces of driftwood and propagate the crypts I have growing in the foreground to cover as much floorspace as possible. Obviously it’s going to take a while to get to this stage.


The cloudyness was bad but at this stage i’d been working on the tank for five and a half hours straight and was getting tired so I didn’t do a water change so I dosed the tank with Prime and restarted the filter.

Testing the water showed zero readings for Ammonia and Nitrite so I let the tank sit for about an hour. After an hour I did another test and again readings were zero.

Happy with this I started transferring the fish over and watched them for about half an hour to see if there was any adverse reactions. Everyone seemed happy enough so I gave them a small feed and went to bed.

Day 2: 21st February, 2009

The tank was noticeably less cloudy the next morning.

I did a water test and got a reading of 0.25 ammonia and 0 nitrites. Figuring I might get a mini cycle due to removing all my old gravel I had placed some in a mesh bag in my quarantine tank as a backup to help the new gravel get seeded.

At 0.25 ammonia I wasn’t too worried so I left the tank alone for the day. I usually feed the fish twice a day but decided with ammonia showing i’d drop to once a day. I tested the water again in the evening and found it was still at 0.25. I did a 50% water change and left the tank for the night.

Day 3: 22nd February, 2009

The tank was much cloudier today then the day before. With ammonia levels present I put this down to a bacteria bloom, either from the soil (soil contains bacteria itself) or the filter.

I did an ammonia test and found it had risen to 1 overnight with Nitrites still showing 0. Not happy with this I did a 50% water change and decided if I still had ammonia climbing the next morning that I would get some more fast growing plants to help absorb the excess ammonia till the tank had settled.

Day 4: 23rd February, 2009

Having a bit of money problems at the moment so I had to stretch my budget as far as I could plant wise. For $20 I managed to get 2 wisteria bunches and 5 chain swords to help with aerating the substrate.

The water cloudiness has gone so I guess the bacteria has settled down again. Unfortunately i’m still reading Ammonia at 2 with 0 Nitrites. I’m going to monitor Ammonia daily till it settles down, nobody is showing any signs of stress so i’m going to leave the tank to settle.

Day 6: 25th February, 2009

My ammonia has started to drop, today I read Ammonia at 1-1.5, Nitrites have started to register at 0.1. At this stage i’m putting it down to a mini cycle most likely because of the change of gravel. All the fish are doing well at this stage.

Day 12: 3rd March, 2009

Ammonia and Nitrite have dropped to 0, Nitrates is sitting at 20. Green algae has broken out due to excess nitrate and is trying to take over the glass but the clean-up crew (6 apple snails and 2 bristlenose plecos) are keeping it busy.

It’s taken 12 days to get over the mini cycle but already the results are looking promising. From here I’ll keep the tank progress updated with monthly updates under the ‘Walstad’ section of the blog.

For anyone who’s considering setting up a Goldfish Walstad tank i’d say go for it. I’ve found the method to be infinately better then a bare gravel setup and probably the best way to keep plants and goldfish together.