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".
I'm not contradicting @dwalstad. I'm quoting her. Or, at least paraphrasing her: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...
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.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.
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!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.