I have a 54 gal corner with 2 clowns, a mystery wrasse and a pinkbar goby. My tank had been running for about 3 months and everything is doing real well. I got the mystery wrasse and goby about 20 days ago and haven't added any fish since, just a cleaner shrimp and a bunch of corals. Would it be safe to add maybe a sandsifting goby or should I wait a little mor?