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Suitable soils for the Walstad method

420K views 734 replies 161 participants last post by  Michael 
#1 · (Edited by Moderator)
"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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#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?
 
#269 ·


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.


Excellent thread! I read all of it, but couldn't find the answer to a question, hopefully I didn't miss it along the way:

When mixing the soil 50/50 with a high CEC substrate, should the mix still be at a 1" depth capped with 1" of inert substrate? I have mixed Miracle Grow (soaked/rinsed 3-4 times over 4-5 days, then spread out to dry once) with Eco-Complete at a 50/50 ratio, so I'm wondering if I can make the depth 2" with the mix and maybe add a thin cap or do I go 1"+ 1"?
 
#3 ·
this is what i usually do. soak the soil, let it get sedimented over time (not so long perhaps 12 hours) than we will get the floaters which usually wood peat. throw the wood peat. and than drain the water to the level of the soil. and than take a gulb of this wet soil cover it entirely by a piece of napkin, than compress it with hands. it will form a toy clay like material, and when it is used in tank usually it will mess the water very minimal. i dont know if this method will make anaerobic condition or not (because we compress it i think it will be more difficult for the soil to get aerated) but so far i have 3 tanks setted up with this method, and all of them have a good growth. i also add a little clay for this soil like 1:7 ratio ;)
 
#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?
 
#7 ·
in indonesia it is way more easier to get a "home made" top soil than getting the branded one. for 50 cent u can get 10 kg of it. but usually they use cow dung for the fertilizer. so usually i use the soil in my garden first for like about 6 month before i use it for my tank ;)
 
#9 ·
Michael,

This is an ambitious thread! Thanks for starting it.

I've maintained "soil-based" tanks for at least 10 years, generally with some success. I use the cheapest bagged "top soil" that I can find. Then I "mineralize" it.

"Mineralization", in this context, means the conversion of the organics in the soil to minerals that are available to the plants, and in a form that doesn't lead to algae and other problems.

I mineralize the top soil by soaking it in a pail of water for a week or so, with several water changes. Unwanted material floats to the top and is easily removed. I rarely have any algae in new tanks, and when I do it is always BGA which often disappears on its own in a week or so.

My problem with MGOC is that it has too many organics, and as you noted, it can cause problems. I have a bag of it here and I'll use it eventually, but I'll mineralize it first and, after that is done, it should be about the same as the cheap bagged topsoil. So why bother with it?

(Diane can grow any plant anywhere with anything, so the rules that apply to most of us don't apply to her. :) )

If anyone disagrees with my definition of "mineralization" or anything else that I've said, I hope that they'll post their comments.

Bill
 
#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?
 
#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!
 
#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.
 
#15 ·
Michael, thanks for this thread. I'm a new member and want to know yours, and others, thoughts on the following. I'm just starting my journey into npt/Walstad/el natural tanks, and want to start with an experimental 10 gallon tank followed by a local north american biotope in a 30 gallon. The 10 gallon tank will be my first Walstad style tank and I want to experiment with different setups and see how they age. Would it be a bad idea to start with soil from a garden compost, mineralize it, then mix it 1:1 as recommended above? Would it make sense to take soil/sediment from the lake for the eventual biotope and do the same? Or is it really better to start with a consistent bagged soil that has worked for others?
You may assume I basically understand what I'm doing in terms of planting and stocking the tank... I'm just trying to avoid any obvious mistakes with setting up the substrate. I'll try to update with progress as I'm learning.
Thanks again!
 
#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.
 
#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.
 
#19 ·
Great topic Michael. I hope others start to post their experience using specific soils soon.

In another thread you mentioned that less experienced hobbyist should stay away from "Hot" soils. When you said "hot" did you mean something like straight MGOC, that has not been mineralized? Or perhaps you meant high organic content soils in general? Such as when you stated this earlier in the thread.

"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."
 
#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.
 
#21 · (Edited)
Micheal, I really appreciate this thread. I've been reading Diane's book and trying the Walstand method for the last 5 months with really negligable success. Your explanation of Miracle Grow and mineralization has been the clearest yet. Maybe a set of important criteria to compare could be formed and put in a chart form for a sticky (ie, cost, handling, plant growth, algae, etc)?

I've been experimenting with several soil option and here's my experience so far (newbie):

1) 20gal community tank with native Chicagoland soil (4mo old). Fish ok (only lost one), snail deaths, and water quality fine but horrible algae problems -- black, green hair, red, and overwhelming brown algae continuously for 3 months. Stem plants rot out; rooted plants don't grow. Messy to work with and adding plants makes a small mess. Cheap. (Excavating crayfish and overly large soil depth likely big parts of issues. T5HO output lights only. HOB filter.)

2) 1L Vase of same Chicago soil in sunny window with Naja grass, no filter -- grows like crazy (4mo old). Snails, no fish.

3) Fluval Substratum: easiest to work with; no discoloration of water. Still takes a long time to cycle the tank. Plants healthiest of all tanks so far. No algae. Very expensive -- $30 for 10gal tank. Nitrates super high at 180, KH 0-17. HOB and single T8 light. Cherry shrimp, floating plants, a few val and anubias nana. No plant deaths; many new leaves; floater sent roots into the soil quickly.

4) 4gal Vase with homemade mineralized topsoil (Scott's) with 10% grey clay, egg shell for CaCO3, epsom salts for Mg+, light salt for K+. Sunny window. Anacharis, val. Up and running 10d and ammonia and nitrites very high at 4.0ppm and 1ppm. No fish, no filter. Mineralized soil: cheap, time-consuming, adding clay makes handling easier as more gelatinous. No big poof of dirt when moving or adding a plant. Customizable with various minerals/ferts. Minimal water discoloration.

5) 1.8 gal betta bowl and 20gal snail tank with Miracle Grow. Lots of floaters, really yellow water regardless of water changes. Amazon sword rotting immediately. Val seems to like it. Mondo grass fine. Middle of road price, requires too much rinsing to make it worth it as a substrate. Tried mineralizing Miracle Grow -- lost 80% in the process; expensive loss and still very yellow water. I will avoid Miracle Grow in future.

Summary: mineralized soil with clay has the best handling for me short of buying commercial (Fluval) -- no yellow water or dirt poofs. Most time consumming though labor-wise and need to plan your tank far in advance (not overnight instant set-up with this method -- takes 7-14d to make) but customizable with one's one additives. Started with 80lb topsoil and ended up with about 25lb mineralized -- topsoil must be mostly water and mulch?

All these tanks regardless of substrate have cycling issues -- have yet to see 0 ammonia and nitrite in any of these set ups. Not sure I'm seeing the "instantly cycled" effect eluded to in "The Ecology of the Planted Tank" book -- still having to do water changes to keep on top of the nitrate cycle. Are others still have long cycles even with soil substrates?

Sorry for the super-long post -- needed to vent about this method a bit; low-tech but not low-maintainence in my hands. Will continue my experiments in hopes of finding what works for me -- going to try the 50/50 mineralized:clay mentioned about as well as different types of clay and see what happens.
 
#22 ·
Using soil in my own little 1g experiment bowl, I found that even "old" soil I took from my flower garden, that I would presume had been mineralized from years of exposure to weather, grew a massive amount of algae, even when planted with a ton of trimmings from my other tank right from the beginning. I shudder to think what would have happened in a larger tank I actually cared about keeping presentable! (Granted, I did no maintenance but top-offs for something like ten months, so maybe the horrifying algae was due to me not changing water at all...)

However, I just had a thought: I use canister filters on my tanks, and when I do a major sponge-squeeze, I get quite a bit of organic material out, most of which is very fine and probably well along the way to becoming humus. I wonder what would happen if I found some way of drying and saving it? Shouldn't it make a good substrate supplement, since it's composed primarily of solid fish waste? It would take quite a long time to build up enough of the stuff to use as a substrate itself, but I doubt it would be very "hot" material. Am I correct or totally off base? :)
 
#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.
 
#24 ·
One of the problems in using "wild" topsoil from a garden or elsewhere is that one does not know what is in it. Gardens are often fertilized, and even if they aren't, there are many sources of organic material that can become part of it.

If one does use "wild" topsoil, IMO it should be mineralized for a week or more, as described earlier in this thread.

When I set up a new soil tank with well mineralized soil, I add a few fish as soon as the water clears, a day or so. I've never had a problem. I think mineralization is the key.

Bill
 
#25 ·
I have to admit... I've never quite understood why ammonia release is seen as such a bad thing...

Personally, I just take it into account as something to expect and make it work for me...

Great source of nitrogen that plants will use through passive intake, and it gets your nitrogen cycle going without having to expose fish to an uncycled tank.

Personally I view it as one of the advantages of soil. Not a drawback.

Mind you I start new tanks very slowly and introduce fauna pretty late and pretty slowly.
 
#27 ·
I'm aware of that, and I have had algae in early stages of soil tanks before. But it always recedes on its own once things stabilize.

I've also started up tanks and jars that had nothing more than a dusting of diatoms during their early stages despite there being ammonia in the water. Also receded on its own.

Not that I don't agree the link between ammonia and algae exists, just that given my own experience and the lack of a chapter in Walstad's book discussing the importance of soil mineralisation, I feel a little differently about it than others seem to is all.
 
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