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Walstad Method modified for Goldfish


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The Walstad Method is a low maintenance way of keeping fish, snails and plants in a balanced low tech system. The fish provide fertilizer and CO2 for the plants. The plants filter out nitrogen and other toxins and provide oxygen for the fish. It uses very little mechanical filtration and minimal water changes.

The downside to this system is the need to keep a relatively small number of fish that won't eat the plants or root around in the substrate (aka goldfish). Here is how I modified the Walstad Method in my 125 gallon tank for the needs of my three red and white comets.

Main Difference #1: Heavy Filtration. While the Walstad Method uses minimal mechanical filtration, I'm using three HOB filters rated for 180 gallons for my 125 gallon tank for several reasons.

1) To provide amble and continuous oxygen for my active goldfish. One feature of the Walstad Method is that oxygen levels lower at night when the plants can't photosynthesize, while CO2 levels rise. This can potentially stress your fish.

2) To provide a water flow that pushes the floating plants toward the front of the tank in order to let light through to the heavily planted back third of my tank.

3) To maintain a backup source of biological filtration just in case the plants can't handle any excess fish waste or decomposing organics.

4) I like having those six little waterfalls flowing into my tank. It also helps to keep the water moving evenly through the tank to keep everything well mixed.

Main Difference #2: Moderate Water Changes. While the Walstad Method uses minimal water changes, I'm doing 20% changes every week or two, although this could probably be reduced to every three or four weeks. But I'm only vacuuming the gravel across the front third of my tank, and letting the fish pooh filter down into the dirt wherever there are or will be roots. I also use this opportunity to do a culling of excess plants and clean out any wilting leaves.

So here are what I would consider to be the essential points in a Walstad Method modified for Goldfish.

1) About one inch of Organic potting soil covered by about one inch of gravel. The dirt will provide nutrients for the plants and the gravel will help keep the goldfish from uprooting them. I used a larger sized gravel than Walstad recommends which seems to work great.

2) Floating plants! The amount of submerged plant growth you get will be limited by how much carbon is in the water. Floating plants or plants that grow out of the water can get their CO2 from the air and can easily outcompete algae. I've found that water lettuce, frogbit and water sprite have worked the best with my goldfish.

3) Plant a large variety and amount of plants from the start that goldfish are less likely to eat or uproot. Let these establish for a minimum of four to six weeks before getting even the smallest goldfish. If you're going to add larger goldfish, let the plants establish and grow even more. Remember you'll need an inch of roots just to get down into the actual dirt.

I've had the most success with Amazon Swords, Jungle Val, Spiral Val, Wisteria, Anubias, Java Fern, Crypts (Wentii and Balansae), Onion Plant and Umbrella Plant. You want to start with large plants with the largest roots possible.

4) Nerite snails. They do a great job of dealing with any algae you might get and breaking down wilting leaves or missed fish food into dissolved organics that the plants can directly use, or that can more easily filter down into the dirt.

5) 10 to 14 hours a day of light. As long as you have floating plants you can leave the lights on for 14 hours to trigger maximum plant growth. The super bonus is you get to enjoy your fish all day long.

6) Moderate water changes of maybe 20% no more than once a week works well and you can probably do much less. Plants secrete a variety of chemicals that inhibit algae growth that you don't want to completely remove. You also want to keep the dissolved organics in your water because some of your plants can get nutrients and even carbon from it. Large water changes will remove these key advantages for no benefit.

7) Ample meals. Give your goldfish fresh spinach or lettuce on a veggie clip often and feed them heavily on a good variety of different foods several times a day. My fish get Omega One pellets, Wardley flake food, peas, Repashy Super Green and frozen plankton.

8) Don't overstock. I would recommend only two to three goldfish in a 55 to 75 gallon and three or four in a 125 if you intend them to grow to a normal size. As long as you have enough healthy plants your nitrogen tests should always be 0-0-0 and you should never have to scrape algae. If you add too many fish for the plants to handle the system will become unbalanced and stop working as intended.

Anyway, those are my thoughts and experiences. I hope they help anyone who wants to set up a dirt planted goldfish tank.

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I think you were really smart by establishing your many plants ahead of time before introducing small goldfish. Your information is very helpful should I decide to get ambitious and venture into establishing a dirted tank via the Walstad method. Thank you! How are your fishies doing?

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This is a cool method and all, but with goldfish, they need at least a 50% water change weekly to refresh the nutrients in the water and remove anything that is un-testable with the standard aquarium tests.

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No they don't Mikey. Our guidelines recommend a weekly water change of 50% or more. That is a guideline for typical aquariums, not a law of nature or a requirement of goldfish. There are healthy goldfish (and koi) in ponds that are decades old which have never had a water change by anything other than rain and overflow. Ponders recommend a 10% weekly water change. Aquaponics systems run water from fish ponds through filters and plant beds and back to the pond. One of the values of such a system is water saving. In the absence of rain, you only need to add enough water to replace that lost by evaporation and from cleaning the filters. The more naturalized a system the less need you have for filtration and water changes.

I have heard that mineral replacement by water changes idea many times. I have never found a person who could identify a single mineral that was used up by fish and needed replacement. The "untested" chemicals in water are generally plant food.

Andrew, IMO if one made a scale on which pure Walstad was a zero and a heavily planted dirted conventional goldfish tank was a 5, this set up is about a 4. Only the low water change keeps it from being a 5.

How long has your tank been running? Long enough to consider it a stable ecosystem? If it were my tank, I would do two things to make it a more natural and thus more sustainable ecosystem. Rather than all those HOBs, I'd use a pond-type filter like this. By filling the top with land plants, you provide another level of biofiltration. By putting the pump at one end and the filter return at the other end, you get a natural, gentle "river flow." By emptying the filter once a week, you get a nice, small water change.

Water changes of 20% at a time are not natural. In nature, water changes in ponds or lakes that goldfish like occur almost continually. I use continuous water change in all my ponds, and when I set up an aquarium, I use it there too. All you need is a container with a dripper to add the fresh water and one of uarujoey's overflow contraptions to remove excess water. Continuous water change eventually produces a steady state chemical environment, and this is one of the conditions of a stable ecosystem. Goldfish like change as much as do old men, and they love a steady state environment.

I would not be concerned about plants using oxygen at night. That happens in nature and the fish don't need aeration. Sleeping goldfish need very little oxygen. There are conditions in which green water algae can reach levels in which they deplete oxygen at night and if this is combined with temperatures over 100F, people find their pond koi dead in the morning. Even those conditions rarely harm comets. Goldfish are native to ponds and lakes. While feral goldfish have been found in rivers, they strongly prefer the still backwaters, not the flowing water.

I really like your tank ideas and am eager to see PICTURES!

(Oops, I see you have them in your other thread. Very nice.)

Edited by shakaho
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Sharon, I believe that what is needed to be replaced regarding minerals are the same minerals and trace elements that we replace when using an RO system, which without replacement can lead to poor osmoregulation. This is how I understand it, though I could be wrong.

You use ponds as an example of why water changes aren't necessary. However, this aquarium is not outdoors and does not have access to rainwater and other resources to replace these. While it is likely that the elements can be replaced by the substrate in the tank, wouldn't those also run out eventually? I think that's what makes those continuous-change systems so awesome. Everything is a steady state, including the minerals, etc.

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Goldfish keepers use water that is vastly different in mineral content, and almost all of it works just fine. Like fish, we need minerals. Do we get them from our water? While some people enjoy drinking mineral water, we can do just fine on distilled water, since we get minerals in our food. If there was a mineral fish needed that was not in commercial fish food,someone would immediately make a fish food that contained it and advertise that they were the only company that did so. Rainwater is (sometimes contaminated) distilled water. It does not provide minerals.

Why do ponds need less water changed than aquariums? The first reason is better filtration. Aquarium filters are too small to remove much more than particulate matter and ammonia/nitrite. If you have a pond upflow biofilter that has 1/10 the volume of your pond and fill it with biomedia, you have major biofiltration. The filter supports not only nitrifiers and other bacteria, but a huge population of protozoa and tiny animals that eat particulate waste, bacteria, other microbes, and act like micro filter feeders. When you put plants in the top of the filter, you add phytofiltration. They gobble up nitrates, phosphates, and a wide variety of dissolved organic compounds.

Secondly, you have the complex biosystem that forms on the floor and walls of the pond. This is opaque, so it is removed from aquarium glass. This biofilm contains most or all of the microbes of the filter plus algae and photosynthetic bacteria. It also functions in water purification. Unfiltered ponds may have green or ugly-looking water (some are nice and clear), but fish can do very well in them, particularly if you have floating and marginal plants in the pond.

Thirdly, ponds usually have a much higher surface area to volume ratio than do aquariums. This provides for better gas exchange, which includes a lot more than oxygen and carbon dioxide. This benefits beneficial microbes as much as it does fish and contributes to water purification.

All of this holds true for an indoor pond as well as long as you provide lighting to support the plants. It is almost all transferable to an aquarium if you limit glass cleaning to the front of the aquarium and use a shallow one.

The purpose of water changes is to remove undesirable chemicals from the water. The more of those that are removed naturally, the smaller water change you need. Standard aquarium filters don't remove much of them.

I think a major reason people have had trouble using a pure Waldorf system for goldfish is that the goldfish destroy so many plants, either eating them or digging them up. Feral goldfish thrive in natural ponds, which are characterized by marginal plants in the shallow water. Imitating that feature makes the system much more workable.

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Thanks for the comments everyone.

By "natural" I meant an environment more like what goldfish/carp have typically lived in for the last several hundred/thousand years: dirt, rocks, submerged wood, aquatic plants and invertebrates with fairly stable or at least slow changing water conditions full of dissolved organics.

I suppose the main thing (other than size obviously) my system most misses would be algae for the goldfish to eat -- but I can live with that -- that's what the Rapashy Super Green is for.

The way Walstad tried to measure her system was to weigh all the fish food she put in and compare it to the weight of the plant mass she was taking out. I typically take out at least one full cup of mostly green plant mass a week. That at least seems to be more than the mass of fish food I put in, but I haven't tried to weigh it all out.

Btw here is the link to my tank's goldfish blog:

http://www.kokosgoldfish.invisionzone.com/forum/index.php?/topic/116731-andrews-125-g-dirt-planted-goldfish-tank/

And here are some pictures.

tank38.jpg

tank39.jpg

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The way Walstad tried to measure her system was to weigh all the fish food she put in and compare it to the weight of the plant mass she was taking out. I typically take out at least one full cup of mostly green plant mass a week. That at least seems to be more than the mass of fish food I put in, but I haven't tried to weigh it all out.

For that to work, you would have to have dry weight of both food and plants.

Why are you using gravel rather than the sand that would be found in a natural lake or pond? (I'm not saying you shouldn't use it, I'm just curious about your reasons.)

Your tank is beautiful. Your fish look healthy and are very pretty. It looks like you are doing a very good job. What are the tank dimensions?

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