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Discussion Starter · #1 ·
"In general, aquatic plants seem to do well in a variety of soils-clays or loam soils with some organic matter. Indeed, I haven't been able to find any major or consistent difference in plant growth in various ordinary soils. . . . In most instances, substrate fertilization appeared to be either detrimental or not helpful. Best plant growth (under aquarium conditions) often appears to be not in the most fertile soil, but in the one that is the least toxic." Ecology of the Planted Aquarium, p 132.

So many people ask questions about which soils are suitable for use Walstad aquaria, it seemed time to start a thread on just that topic. Here is where we can share our results using different soil substrates.

First, some definitions. "Soil" has different meanings to different people. For our purposes, "soil" means any growing medium intended for terrestrial plants, but which we have adapted for use in the planted aquarium. "Topsoil" has a very specific meaning to soil scientists, horticulturists, and geologists. Often, what is labeled "topsoil" in a bag in your garden center bears no resemblance to natural topsoil as understood by science. Most natural topsoil is primarily minerals, with only a small percentage of organic matter. In our discussion, we should use the general term topsoil to refer to naturally occurring surface soil. When we are talking about a specific commercial product that has "topsoil" as part of its name, we should be sure that is understood.

Another term that needs definition is "organic". In this discussion, organic is used in the scientific or chemical sense; that is, material derived from living matter. This organic matter will be in various stages of decomposition. When I use the term "organic" I am not referring to the organic method of gardening, and I most definitely do not mean the undefined marketing hype used to sell so-called "natural" products.

And one last bit of clarification, when we talk about soil in this discussion, we are not referring commercial brands of aquarium substrates, like Flourite, Eco Complete, ADA Aquasoil, etc. Some of these products are very good, and may be useful in the Walstad method. Some are not.

I will start the discussion in the next post. But the only way that this thread can become really useful is if you post your knowledge, experience, and questions too!
 

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Discussion Starter · #2 ·
Miracle Gro Organic Choice Potting Mix (MGOC) is often recommended, and by Diana Walstad herself in her on-line article about small aquaria for shrimp at http://www.atlasbooks.com/marktplc/00388Shrimp.pdf. Unlike many other "potting soils", MGOC has a clear list of ingredients and a nutritional analysis on the bag:

50-55% composted bark
Sphagnum peat moss
Pasteurized poultry litter
"organic wetting agent" (whatever that is)

Analysis 0.10-0.05-0.05
total nitrogen 0.10%
available phosphate (P2O2) 0.05%
soluble potash (K2O) 0.05%
". . .feeds up to 2 months. . ."

This tells us several important things. First, this product is 100% organic matter. Remember, natural soils are almost never 100% organic matter-less than 20% is more common. So this soil is going to undergo a lot of decomposition in the aquarium.

Second, it has chicken manure in it, which makes it much more fertile (higher nutrient level) than most other potting mixes. But, these nutrients come from slow-release organic sources, not synthetic inorganic chemicals. Not that there is necessarily anything wrong with synthetic fertilizers, but they behave differently when submerged than organic ones do. This higher fertility is expressed in the analysis (which shows much more nutrients than typical for potting mixes or natural soils) and the last statement, "feeds up to 2 months".

What does MGOC look like when you open the bag? It is dark brown, with a mix of fine particles and some pretty big chunks of not-yet fully decomposed bark. These chunks are a source of concern, for several reasons discussed below. I did a quick test with a ¼" soil sieve, and about 20 to 25% of MGOC will not go through the sieve, even after rubbing it hard with a gloved hand.

MGOC has three major advantages:
1. It is a nationally available product
2. The ingredients and analysis are clearly listed on the bag
3. It is relatively consistent no matter where you buy it. (Many other products vary greatly from one region to another.)

Used straight from the bag, MGOC has four major disadvantages:
1. The big pieces and many of the smaller pieces float, which can make a big mess if your cap is not heavy enough, or if you change your mind and move a plant.
2. The high nutrient content usually causes an ammonia spike in the first month following tank set-up.
3. The partially decomposed bark releases a lot of tannins into the water. This is not usually harmful to fish or plants, but the tea-colored water may look bad to you.
4. Because it is 100% organic matter, if the soil and/or cap is too deep, the soil layer may become very anaerobic. This is bad for many reasons.

Fortunately, there are easy ways to deal with all of these disadvantages.

The simplest ways are a thin soil layer, patience, and water changes. This soil is hot stuff, you do not need much! How deep a soil layer to use depends on size of tank and types of plants, but I would never use more than 1.5". For beginners and small tanks, 1" or less is plenty. Patience is necessary to allow the biological filter to develop properly and absorb the ammonia. Water changes help with that, and also remove the tannins. Eventually the big pieces become saturated with water and no longer float.

The more sophisticated ways to deal with these problems involve processing MGOC in some way before you use it. A quick and effective process is "soak and drain". Put the soil in a big bucket, cover it several inches with water, and stir well. Let it sit over night, then carefully pour off the floaters and the brown water. Fill, stir, and let sit over night again. Repeat the soaking and draining cycle until you see no floaters and the water is reasonably clear, or until you can't wait any longer, LOL. Seriously, three complete cycles is usually enough to make a big difference. This method will result in a loss of total volume of soil of 25-30%, so start with more than you need for the tank.

Another way to process MGOC is to mineralize it. This process is described fully in several great threads in the library forum. Mineralization greatly speeds decay of organic matter into a very stable form called humus. Humus does not release ammonia into the water, and is unlikely to become anaerobic.

And there is one last tip for using MGOC or any other highly organic soil: mix it with an inorganic substrate that has a high cation exchange capacity (CEC). Examples are laterite, Flourite, Turface, plain cat litter (no perfume, antimicrobials, or clumping agents), and Safe-T-Sorb. Remember, natural soil is almost never pure organic matter. Mixing the organic matter with inorganic high CEC substances means that the ammonia and other nutrients produced are held in the substrate where plant roots can use them, but where they will not harm fish. And by reducing the percentage of organic matter, you reduce the likelihood of the soil becoming anaerobic. I like a 50/50 mix. Phil Edwards first gave me this advice, and it has worked well for me.

Let's hear from eveyone else! What kinds of soil have you used in your Walstad tanks, and how well did they work?
 

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Discussion Starter · #4 ·
Compressing the soil with a cloth will not cause it to become anaerobic--you are probably just squeezing out the excess water.

Adding the clay has the same effect as mixing with an inorganc high CEC substrate. Most of these are just fancy forms of clay. And the mineralized topsoil (MTS) process includes adding clay if the soil doesn't have enough to begin with.

Thanks for sharing your method. What kind of soil are you starting with?
 

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Discussion Starter · #10 ·
Bill, I agree that the 100% organic make-up of MGOC is the cause of most problems with using it. The added nutrients from the poultry manure just make it worse. Yet because it is so frequently recommended and widely available, I thought it best to start the thread using it as an example.

Recently I've used high-quality homemade compost from a neighbor, mineralized it, and have very good results. But I still mix it with Turface or Safe-T-Sorb so that the soil part of my substate is not 100% organic.

What brands of "topsoil" have you used, and where did you buy them?
 

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Discussion Starter · #12 ·
Yes, for our purposes the additives are almost always bad!

The generic, off-brand topsoils can vary a lot from region to region, and even from one season to another, depending on what materials are available. What I would love to know is, has anyone had problems from using any of these generic soils?

I find that same clay-like soil in my old tanks. My guess is that it is the stable mineral components of the soil I started with, plus humus from decayed organics. The organics come from the original soil, and from all the biological processes that have been going on in the tank for the entire time it was set up. A further guess is that it is relatively low in nutrients (used up), but still has a high CEC.

Funny you should mention it, but I just took down a tank over the weekend, and that old clayey soil was packed with roots from the pigmy chain sword that had taken over the tank. I have new respect for the roots of that species!
 

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Discussion Starter · #14 ·
Humus is organic material that is thoroughly decomposed, so that you can no longer tell what it was originally. It is extremely stable, and can remain unchanged for hundreds of years in the right conditions. It is not high in nutrients, but it does have excellent CEC and provides a great surface for the growth of beneficial bacteria. Some kinds of peat are humus.

A Google search or Wikipedia will give tons of information about humus.
 

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Discussion Starter · #16 ·
Alden, you are welcome, and please let us know how your tank turns out!

I think either the garden compost or the lake sediments would work. As mentioned before, I've used compost made by my neighbor who is the local vegetable gardening expert. He runs his compost material through a chipper/shredder that produces very fine particles to begin with, then takes it through a hot composting process, then grinds it again. (He is my compost guru, LOL.) It mineralizes very well, and gives me good results.

One of our very knowledgable members Phil Edwards worked at an aquatic vegetation research facility while doing his PhD. One of the research ponds had what he called "magic mud", a silty sediment that grew aquarium plants better than anything Phil had ever used. So if your lake sediment is already growing plants in situ, it should be fine for aquarium use. You would probably want to take it through some wet-dry cycles to help eliminate weeds and pests.

Setting up a test tank is a great idea. You can actually do something much smaller, like a gallon "fish bowl" or jar. I do a lot of these things just to propagate plants, and try different substrates. You can usually get a good idea how well a particular substrate works within a couple of months. And you can test efffects on animals by putting in a few snails, shrimp and/or guppies.
 

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Discussion Starter · #18 ·
Thanks for reminding me of the famous dog poop tank! As you say, I would not recommend it, but it really does put many of our anxieties about soil into proper perspective. In other words, don't worry so much.

Dogfish is also a member of APC, maybe he will pay us a visit.
 

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Discussion Starter · #20 ·
Sorry, that is terrestrial gardener's slang.

Yes, I would classify MGOC as "hot" because it is 100% organic matter that is not fully decomposed AND it has a high nutrient content (for aquarium soil).

A soil that is 100% humus would not be hot. It is still 100% organic matter, but nutrients are low and it will not decompose much (if at all) in the aquarium.
 

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Discussion Starter · #23 ·
Jmn, thank you, I am glad it is helpful. And I am sorry that you have not had much success so far. I had a very different experience--my first Walstad tank was a great success (after the ammonia spike, see below).

I always go through a "cycling" period when I set up a new tank. MGOC straight from the bag was the worst, it took a month before the tank was safe for fish. Processed MGOC was better, and the easiest/quickest was mineralized soil mixed with Turface or Safe-T-Sorb. I have not used Fluval Stratum.

One of my complaints about most commercial substrates is that their ingredients and manufacture are secrets--try to find out what is in Stratum or Aquasoil. My best guess is that those two products are actually very similar, and both produce an ammonia spike in a new tank.

I think Diana Walstad gets away with putting fish in a tank right away for two reasons. First, she really stuffs the tank with healthy, fast growing plants right from the beginning. This is critical. For those of us who do not have access to our own plants or really good plants in large quantities from other hobbyists, it is difficult to plant a new tank densely enough with healthy plants that will start absorbing ammonia from the water immediately. Limp, sickly plants from the Petsmart, or plants traumatized by shipping just are not the same.

Second, Walstad is an expert! She watches the new tank carefully, and is prepared to do large water changes quickly if she sees subtle signs that something is going wrong. I'm not that good.

A few questions:

How many T5 HO tubes are you running over your 20 gallon? Honestly, I think more than one is probably too much light, and the likely cause of your algae problems.

What is your native soil like in Chicago?

You mention mondo grass, did you get this at a big box retail place? It is actually Ophiopogon japonicus, a terrestrial plant that will last for a fairly long time submerged, but usually rots. (To be fair, some people say that it survives long term and even grows, but I remain skeptical.) I hate the fact that such places sell it for use in aquaria.

Your comment about the Scott's is interesting. I haven't tried the "Premium Topsoil" in a full set-up yet, but one of our other members has worked with it a lot, and will give us a report pretty soon.

Thanks for the post; a post with good observations and good questions is rarely too long.
 

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Discussion Starter · #30 ·
Bruce, I do a lot of these little "patio ponds" outside every year. The progression of your pot is pretty typical for them. I usually put the plants in shallow pots, but the principle is the same.

Strong rooted plants will definitely keep even a rather deep substrate from becoming anaerobic. Water lilies are the best.
 

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Discussion Starter · #33 ·
Jeremy, welcome to APC!

In a sense, I think we are all talking about the same thing. I've always thought that "mineralization" was a somewhat misleading term. It does not convert the organics into a truly mineral (inorganic) form--that requires high heat or other means of chemical change. It does rapidly decompose fresh or incompletely decomposed organic materials into a completely decomposed, stable form called humus. Humus is the term usually used for the solid form found in soil. Humus can also be dissolved in water, in which case it is sometimes called "humic substances" or "dissolved organic carbon" (DOC).

This rapid decomposition occurs best in a moist, oxygen rich environment. For practical purposes, the wet-dry cycles are the easiest way to accomplish this. But the same type of decomposition can and does occur submerged, as long as oxygen levels are high enough.

Some time ago I read of a method for producing liquid fertilizer for terrestrial plants from poultry manure. Poultry manure is very "hot" and will "burn" (damage roots) if applied directly to plants. Simply described, you put a few handfulls of poultry manure in a bucket, fill it with water, and drop an airstone in it. The manure is suspended and constantly mixed with oxygen rich water. It breaks down a becomes usable in a few days to a week. Since I keep chickens, I tried it and it works. It was too messy and smelly for me, but in large scale poultry farms with proper equipment it is very effective.

So, if while soaking your soil you keep the oxygen levels high in the water, you can "mineralize" the soil while it is submerged.

Again, back to practicality. Most of the effect of ordinary soaking and draining is to simply remove the excess nutrients by dissolving them in water and pouring them on the lawn. But some aerobic decomposition does occur while oxygen levels are high enough in the water.
 

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Discussion Starter · #41 ·
Rivercats, welcome to APC!

Sounds like a great tank you have going. If there was no other source of fertility, my guess is that the soil would be exhausted in 6 months to a year. But I suspect there are some fish in there, lol, and with fish comes fish food.

Diana Walstad demonstrated through chemical analysis that fish food contains all the nutrients necessary for plant growth. So if you have just moderate fish population and feed generously, you should be adding enough nutrients so that the soil will absorb them by CEC, and hold them until the plant roots find them.

In this way, the soil never becomes depleted. Even when the initial supply of nutrients are used up, the soil never loses its CEC, so it always has the ability to absorb nutrients from fish food and any animal waste in the tank.
 

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Discussion Starter · #45 ·
Rivercats, I don't fertilize at all--not in the water column and not in the substrate. I don't know anything about the commercial aquarium substrate fertilizers, but I do use Osmocote for my pond plants, and many use it in aquariums.

You have plenty of fish. This is going to sound like a funny question, but do you also have snails in your tank? One of the reasons I get away with feeding my fish generously is that I have lots of snails. They do a great job of converting extra fish food into a form that is not as likely to cause water quality problems and is good plant food--feces.
 

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Discussion Starter · #47 ·
Cool! I actually farm snails for my paradise fish, striated loaches, and assassin snails. But I don't have any Malaysian trumpet snails (MTS)--I keep asking, but no one will give me any!
 

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Discussion Starter · #50 ·
Thanks, jmn, but that won't be necessary. I am SURE that someone here has some, even if I have to clean tanks at the LFS, lol.

I don't know for certain if they make a mess in soil substrates or not. I was going to try them in a Walstad nano where I also keep assassin snails, figuring that they couldn't over-populate in that situation.
 

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Discussion Starter · #56 ·
Great post! I have a similar post you made long ago bookmarked. That test is how I determined that my native topsoil is unsuitable for aquarium use--large percentage of colloidal clay.
 
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