I've read the recipe for mineralized soil substrate, and to use 3M color quartz, flourite, ecocomplete, or just plain inert aquarium gravel for a "topping" or "cap" substrate. I prefer the appearance of pool filter sand, but I'm concerned that it will eventually mix/blend with the soil beneath. 3M has stopped manufacturing color quartz, and some other company is selling a substitute. I have located (2) 50 lb bags of 3M Colorquartz Black, grade "T", and have it "reserved" for my purchase. I'd appreciate any comments or info, prior to my investment in the build up of my second planted aquarium. Thanx!!!