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I'm not disagreeing or agreeing but the post above mine by Diane has:

"Remember that clay is composed of aluminosilicate, meaning that all clays contain aluminum and have the potential to generate aluminum toxicity."

which seems inconsistent with your statement or perhaps i am misunderstanding something...

Calcined clay is similar to porcelain and people have been keeping fish in porcelain bowls for a thousand years. I can't speak for the chemical properties of Matrix and Denitrate except to say that Seachem advertises them both as being "inert".
 

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I'm not disagreeing or agreeing but the post above mine by Diane has:

"Remember that clay is composed of aluminosilicate, meaning that all clays contain aluminum and have the potential to generate aluminum toxicity."

which seems inconsistent with your statement or perhaps i am misunderstanding something...
I'm not contradicting @dwalstad. I'm quoting her. Or, at least paraphrasing her:
For making pottery, clay is fired/heated to 1,000 to 2,500F. The high temperature melts and hardens the clay particles, somewhat like heating sand to create glass. The clay becomes a ceramic, the hardness depending on the firing temperature.
A few of the pots used for her "potted plants" are made of clay. I'm assuming the baking process affects a chemical change of some sort upon the iron.
 

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Discussion Starter · #65 ·
My biggest concern in this thread is introducing toxicity to the tank. When I read the above past about clay contain aluminium or iron it just makes me thing I should stick to inert substrate. The plants might not grow as well but they grow and the fishes don't have to worry about long term poisoning.

I think the biggest question i have given the above comments on clay is how do you know if any of the products are safe for long term use. I realize this thread doesn't seem to focus on fish health but isn't that a concern when picking your substrates ?


In nature, fish are found in lakes with clay sediments and rivers filled with turbidity from clay particles. Neutral pH and oxygen in aquariums and most natural waters neutralize aluminum and iron toxicity. (Iron and aluminum oxides are not toxic to fish, plants, or humans.) Plant roots in anaerobic substrates are the vulnerable ones, not fish.
 

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My biggest concern in this thread is introducing toxicity to the tank. When I read the above past about clay contain aluminium or iron it just makes me thing I should stick to inert substrate. The plants might not grow as well but they grow and the fishes don't have to worry about long term poisoning.

I think the biggest question i have given the above comments on clay is how do you know if any of the products are safe for long term use. I realize this thread doesn't seem to focus on fish health but isn't that a concern when picking your substrates ?


In nature, fish are found in lakes with clay sediments and rivers filled with turbidity from clay particles. Neutral pH and oxygen in aquariums and most natural waters neutralize aluminum and iron toxicity. (Iron and aluminum oxides are not toxic to fish, plants, or humans.) Plant roots in anaerobic substrates are the vulnerable ones, not fish.
Thank you for this explanation, Diana. I have page 132 permanently bookmarked in my copy of Ecology of the Planted Aquarium (EPA) and, for whatever reason, it is only clear to me now that you were writing about toxicity to plants, not fish. D'Oh!
 

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Discussion Starter · #68 ·
Thank you for this explanation, Diana. I have page 132 permanently bookmarked in my copy of Ecology of the Planted Aquarium (EPA) and, for whatever reason, it is only clear to me now that you were writing about toxicity to plants, not fish.

If I revise book, I will try to make this more clear. It is certainly an important point, so thanks for bringing it to my attention!
 

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STS (Safe-T-Sorb) is a natural clay (montmorillonite of the smectite clay group) mined in western Tennessee (USA). The company's nearby plant heats the clay to 800 degrees F which produces a calcined clay (clay hardened via melting). That temperature results in a material that is partially ceramic. As such it is very absorbent and effective in soaking up liquids, which is its intended purpose. SEACHEM heats their clay from northern Georgia to a higher temperature (1,200 F) from which they get FLUORITE. (Reference: Neil Frank, noted planted tank expert.)

For making pottery, clay is fired/heated to 1,000 to 2,500F. The high temperature melts and hardens the clay particles, somewhat like heating sand to create glass. The clay becomes a ceramic, the hardness depending on the firing temperature.

Kitty litter is only heated to dehydrate (get rid of absorbed water). Dehydration can be done at much lower temperatures (250F? or 150C). Thus, kitty litter has no structure and rapidly breaks down into fine particles (i.e., mud). Mixed with an organic potting soil, kitty litter mud would be highly reactive--release aluminum to create aluminum toxicity?-- whereas any aluminum release from STS gravel would be much more gradual and controlled, such that plant roots could handle it.

Remember that clay is composed of aluminosilicate, meaning that all clays contain aluminum and have the potential to generate aluminum toxicity. In addition, tropical clays may contain iron oxides and aluminum oxides deposited inbetween clay particles. These oxide deposit can cause even more metal toxicity problems. In my book (p. 132) I describe a tank meltdown experience I had from mixing potting soil with just a little bit of laterite clay. It created iron toxicity.

Michael here describes mixing STS with soil. Another knowledgeable hobbyist reported getting good results potting plants in a mixture of STS and soil. STS has a good reputation from experienced hobbyists, including our very own Michael!
I am a ceramics artist and here is a useful chart on what happens to clay materials (both chemically & physically) when they are fired. It may give you some insight on why STS behaves differently than kitty litter besides the varying chemical makeup. STS appears to be fired just before “quartz inversion” and/or some quartz inversion may be happening.
Font Material property Rectangle Parallel Screenshot
 

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Just posted a revision of my Potted Plant article on my website.

In order to revise my Potted Plant Tank article, I tested the effect of an STS gravel layer on the potential removal of added nitrates. I added 10 ppm nitrates to a 20 gal tank with STS (Safe-T-Sorb) and 10 ppm nitrates to a matching 20 gal tank without STS. Goal was to see whether denitrification or nitrification explained the nitrate accumulation I had observed earlier in one of the 10 tanks described in my article. Over a period of 13 days, I measured absolutely no decrease in nitrates in either expt tank. Attached is file describing the expt testing STS's effect on the added nitrates.

Unexpectedly, I ran into a "lurking variable." The guppies in the expt tank without STS were from an older batch that I believe was genetically less "fit" than the batch in the expt tank with STS. Guppy fitness/age may have explained the deaths that occurred during expt, not absence of STS.
I’ve been thinking about this. Did you use “new” STS straight from the bag? Maybe the STS needs to be “seasoned” by sitting in an aquarium for a while to acquire nitrogen fixing bacteria? Maybe STS straight out of the bag has no bacteria?
 

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Discussion Starter · #71 ·
The STS had been in the aquarium for awhile. You're right that straight out of the bag--after being baked at 1,000+F--it would have no relevant bacteria.
However, I consider the STS irrelevant in my tanks. The plants are taking up the ammonia so fast that it never gets converted to nitrates.
In tanks without heavy plant growth, STS could have a beneficial effect.
 

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The STS had been in the aquarium for awhile. You're right that straight out of the bag--after being baked at 1,000+F--it would have no relevant bacteria.
However, I consider the STS irrelevant in my tanks. The plants are taking up the ammonia so fast that it never gets converted to nitrates.
In tanks without heavy plant growth, STS could have a beneficial effect.
Okay that sounds like a good goal to shoot for. Eliminate the ammonia before it has a chance for mischief 👍
 
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