put sand in there, a rock barrier and excessive filtration and sumbu dwarf comps would work even if you missed a week occasionally. Where are you that you can't get shells? I'll mail you some!! Also a, for sure, pair of Caudopunctatus (look alot like mustax) would probably work cause the males max out around 2.5 inches. They always set up a territory about the size of a 10 gal anyway. They don't need shells though they seem to prefer them, they will also spawn under a flat rock or cave.