I’m keen to add a basic type substrate to a 450L bristlenose brood stock tank, which has always been left with the glass bottom and doing a weekly vacuum with the water change. I’m now adding CO2 to this tank to combat BBA and to keep some of my lower tech plants ultra happy, including a humongous java/mopane outcrop, needle leaf and mosses. I don’t plan to add anything into the substrate, unless I add some crypts and will then keep them happy with some fert pills. Ok, simple question - should I go with say a medium grain silica 2-5mm or river sand ? I was thinking that the silica might be easier to maintain with doing a gravel vacuum when needed and the more tightly packed river sand might result in some anaerobic pockets ? I would not plan to empty the tank to add the substrate, but would simply add it "˜somasoo’ and with doing a 50% water change. What's tempting is I live close to a river with some stunning golden and clean river sand, but which I would have to boil first. Advice from the experts please ?