All I'm going to say is a panther grouper will get awful big awful fast , and won't look like much when it's a foot or so plus.
I would try to get an alkalinity test kit and see if you need to buffer up , and maybe get your pH up a bit.
For 20 high's I like Centropyge argi, Cirrhilabris rubriventralis, banana wrasse and Stonigobiops gobies.