You could keep clowns. There are several other small salt fish you could keep also. A flame angle is a pretty fish and only grows to approx. 3" Some types of blennies or gobies would work.
Yeah a basic FW heating and filtering system works on a tank that small.
Mushrooms are a pretty easy coral to keep.
PH should be around 8.0-8.3....IMO it is more important to keep it constant than exactly 8.2. A constant ph of 8.0-8.3(meaning virtually no fluxuations if possible)
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Clint
CDevoe1111@aol.com