05-09-2013, 02:30 PM
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Flourite and laterite have been used for decades by aquarists, and they are clay.
Clay is great because it is nutrient rich, but the clay particles don't release the nutrients very easily and have a high cec (cation exchange coefficient).
Dense clay can also be used in a much thinner layer, say, 1/2 inch. Peat-based soils hold onto air, which is a great thing in a garden, but tends to float submerged. It also holds onto bubbles in the substrate. I had a OC Potting Soil tank that after a couple weeks started to bulge up in the middle from gas buildup... I then Made the mistake of disturbing it, and the substrate bubble exploded. The hydrogen sulfide was so bad, it was gagging me. I luckily removed the fish fast enough...
I've used clay ever since. I think a clay/vermiculite mix is ideal, but I usually don't mess with the vermiculite.
Also, according to D. Walstead's "ecology of the planted aquarium", the substrate should have a slightly higher pH than the water column, and she reccomends a
Small amount of powdered dolomite limestone (not pelletized lime) or crushed coral.
I don't feel this is neccesary, but many peat products have an easily soluble "pH up" chemical to counteract peats tendency to lower pH.
Geez, didn't mean to write an article...