The OP claims to be a "purebred". If so, shouldn't be asking for ID.
The species name AND collection point SHOULD be known, to claim it as a "purebred".
Therefore................. I sincerely doubt it's a "purebred" ( because you DON'T know its provenance)
I find it ironic and downright...
The Yellow Blaze Afra (Cynotilapia Afra Nkata Bay) might not color up as much because of the other tank habitants, specially with the Williamsi in there. He looks like he is the tank boss.
The only time you have to worry about rocks leaching minerals is if you keep soft water/low Ph species. If you keep neutral or hard water species you shouldn't worry about it.
It is important to check the surface of the rocks for potential exterior chemical contaminants (from road sides...
In my experience the only shelldwelers that readily breed are the Neol. Multifasciatus (Multi's). All the other shelldwellers I have experience with (5 different species), can be finicky about getting to breed. But once they start, they will continue to breed. Keep taking good care of them and...
I was thinking on over OVER-stocked tanks, as in 100 fry in a 30g grown-out tank. Not so much in a conventional over-stocked display tank, which properly filtrated should be enough.