Yes you can still get the fish I mentioned without fights. You don't want 2 male leluepi though....they would fight in any sized tank...I would get 4 small ones and wait for a pair, trade in the others. The brevis will chase off any fish (no matter how large) from their shell, but won't harm them and don't go looking for trouble. Leluepi won't go looking for trouble either, but they will defend their cave. Tanganyikans in general aren't too aggressive (there are some that are).
I meant FW, it would take a long time, and your pH might be high enough to prevent disolving of the crushed coral, and your diggers are probably preventing it also. I am talking a couple of years and it doesn't always happen....depends on how often it is vacuumed, the fish you keep, and your natural water chemistry.