Play sand is not suitable for aquarium use. Too much variability in grain size, it'll pack down very hard, and smaller particles can enter your filter and wreak havoc on impellers. Last point is probably less of a concern with a cap. You should go with either black diamond blasting sand(BDBS) or pool filter sand. If you want to cap that with Eco-Complete, that's fine, but I'd just leave BDBS uncapped. Easier to plant in than Eco-Complete due to grain size.
I, personally, would skip potting soil. Water column fertilization will take care of everything. Plus, if you're like me and are constantly moving things around because you're never totally satisfied and can't leave well enough alone...potting soil isn't for you unless you like a big ol mess
Last edited by mgeorges; 04-23-2018 at 08:31 PM.