Well you could use any type of rock that will make your diy rocks porus. I would stick with pea gravel. It's not to big or to small and I think it looks pretty good. The salt will dissolve when you place the rocks in water thus making the rocks porus.(allows water to flow). The rocks I made were so porus I could turn a hose on full blast and the water would just go right through the rock
. The more porus the better biological filtration the rocks will have. An yeah my rocks were soaking way Before I had any stuff for my tank. I would go out and buy it piece by piece. It does suck to wait but u will soon Learn that with in time it will all work out.