Something smells fishy

[Galvin900]

Lately I have had problems with my tank producing a odor. The smell is like a
fishy smell. The only thing I have done different lately is add Coppersafe &
started feeding the trigger some squid instead of shrimp. This is a 75 gal
with live sand, 10 gal sump, ETS Reef Devil II, with only a trigger & tang
inside.
Any suggestions to rid the smell?