Roka,
I keep the tank a little on the warm side: 82-84F (local ocean temp +/-)
I do water changes with local ocean water.
I try to keep the PO4 and N as low as possible (with water changes, mainly)
When I do collect something, I usually pick a very small invert or fish. That way, I figure there's less chance of introducing something that could cause a lot of damage or take over the tank. If I see behavior that is too agressive, the specimen goes into my sump to isolate it, and then right back in the ocean the next time I go out.
It's worked for me so far... Maybe just newbie luck.
If this Protopalythoa grandis stays happy, maybe I'll try propagating it and selling them back to the local stores... Make some of my $$ back?