If you quarantine new, juvenile fish when you get them, especially Tanganyikans, it’s a good idea to not provide shells for cover. Even if you’re new fish are shell dwellers, hold off on the shells until they’re out of quarantine and you move the fish to your show tank. Why? Three reasons.
First, many new fish are often shy and/or skittish, and will seek any kind of cover available to them. This includes shells, even if the species isn’t a shell dweller proper. For example, juvenile L. calvus, L. compressiceps, and members of the Julidochromis genera have been known to utilize shells. Skittish or shy fish who aren’t accustomed to shells or who don’t use them by instinct may accidentally become lodged in them and be incapable of extracting themselves. If you’ve kept African cichlids long enough, you’ve invariably lost some fish that have gotten stuck in rocks. The same principle applies to shells.
Second, shells provide a sick fish a place of refuge even if it’s not shy or skittish. It may just want to avoid all interaction with other tank inhabitants. This means a sick fish might well lodge itself in a shell and die there.
Third, even juvenile fish may still be aggressive to each other, con-specifics or otherwise. Lacking any other option, the inside of a shell is a place of refuge from aggression.
One thing you should be able to do frequently and easily if you quarantine your fish is account for them. Of all the fish you keep, quarantined fish are the ones you should be watching the most carefully so you can quickly recognize any signs of illness. You’ll want to address any signs of illness as quickly as possible. If you give quarantined fish places to hide such that there is no way you can see them, then you won’t be able to account for them and thus you’ll have no idea if they’re sick until it’s perhaps too late.