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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.
Still inprogress of cycling tank and I've been doing some research on this walstad method. I don't really want to try this method so that my tank is care free but I'm more interested in having a soil layer with light stones on top and some plants to basically have a natural look pluss extra filtration. Butt I'm not to sure if its somthing realistic with goldies.. thoughts? Oppinions?