So we got a 120 gallon fish tank to move our fish into. We got it on craigslist, so it came with everything. Well I have put in the decor it came with and he also had these black rocks I haven't put in yet, I don't know does it look okay? Where should I put these rocks, or should I even use them? We want to put on a backdrop, and were thinking solid black...now I'm not sure... Ideas welcome, please!