Well the way im trying to scape my 30 gal is half pea gravel and half black petco sand. Side by side, not stacked. Im trying to get it to look some what like a shore line. I also have 2 filter types, hob and sponge. To get the most effective filtration which filter should be on which substrate? This will help me figure which half will be sand, since my hob filter is only able to be in 1 spot due to the hood slots. I am assuming that the sponge would be better over the sand, and hob for gravel. But i could be wrong. Maybe it doesn't really matter. But it wouldnt hurt to ask! Also will my plants grow in sand??