One of the biggest dilemmas a goldfish keeper can have is the want to keep healthy plants in unison with your goldfish. The benefits of plants are that they attractive to look at, help with biological filtration and I find allow the fish to display a more natural behaviour.

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.

Related posts that might interest you:

1. Walstad Goldfish Tank Update October 2009
2. Walstad Goldfish Tank Update August 2009
3. Filtering a Goldfish Tank or Aquarium: Undergravel Filters
4. Walstad Goldfish Tank Update September 2009
5. The Walstad Aquarium and Goldfish: My conclusions