sand "cap," substrate depth
I just put down my substrate -- FloraMax (only decent thing they had two bags of at PetSmart) "capped" with National Geographic white sand. The sand cap ranges from 1 to 2 inches on top of about 2 inches of FloraMax. Do those depths sound right? I expect some of the sand will slowly filter down into the FloraMax. I've read about "anaerobic pockets," which sounds ominous, so I don't want to create a high risk of that... if it is indeed a bad thing.
Also, I put the sand cap down for my corydoras, but I suspect manypeople who do that have a plant-based reason for it... what benefits does it have? Just making it easier to hold down roots? Or something else?