Dolomite and calciferous rocks will HELP buffer the pH, but if you are trying to replicate hard water (especially in a large-ish tank) that won't solely do the job. I would just recommend letting that rock do whatever it is going to do and leave it at that... seeing as how (probably) all the fish going in there will be tank bred and can live in practically any water fine... just won't breed.
If you really want to buffer the pH (just advice, but personally I wouldn't), use one of the rift lake buffers by SeaChem... they work excellently. As of stocking...I like peacocks... but I don't have a huge expertise in this so I will let you make your own decisions.
If you really want to buffer the pH (just advice, but personally I wouldn't), use one of the rift lake buffers by SeaChem... they work excellently. As of stocking...I like peacocks... but I don't have a huge expertise in this so I will let you make your own decisions.