125 gallon! I was power feeding my fish for weeks meaning I feed them till they can't eat anymore. I decreased the feeding to a reasonable rate. I have raise Pacus before but never power fed like i have fed the fish in my odd ball tank. I have been trying to power feed so that my Tem can grow faster.
Why are you attempting to keep flagtail and pacu in a 75? Do your researh and get a proper size tank for the fish you are trying to keep.

And what are you plans for the fish after the 125?