I have read the recommendation is for about an inch of sand for substrate. Has anyone tried, or even thought about a plenum. I have tried this for a reef tank and I am happy with the results, but this isn’t a reef, it’s an octo tank. The setup I’m talking about is described in detail at garf.com. Basically there is grate covered by plastic window screen to create the air pocket, then 2 inches of reef sand on top of it. This is covered by another screen, then a couple more inches of reef sand. This second screen keeps burrowing critters from going any lower. Will this be ok for a bimac, or do you think I should just go with 1 inch of sand?