Some seachem liquid calciums have gluconates in them , i was told it actually is a good thing because the coral gets "energy " at the same time as calcium.
what i have personally found on a few occasions , is if you very much overdose ...
The tank gets a bacterial bloom and goes milky .
Its a shocking sight ! , but actually nothing minds it, corals and fish act like nothings changed , and i had the milky water for at least 2 weeks trying all sorts of floculents and fine media and special blend/ stability and nothing helped.
the moment i put on a U.V sterilizer , it went away overnight.
I only uses the sterilizer for this milky bacterial bloom .( which does not effect your ammonia nitrite ect )