The Walstad Aquarium and Goldfish: My conclusions
Back in February this year I decided to tear down my existing filter+gravel substrate fish tank and attempt to run a Walstad planted aquarium with my goldfish.
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.
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.
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.
February 2nd, 2011 at
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