I'm a little bit fuzzy on how a GFCI works in that it either implies power on the ground wire and thus a "leak", or whether there is an imbalance between hot and neutral and thus a "leak". Either way though, I'd say it's not good. I would look at that mag 7 and see if there's anything wonky with the wire where it attaches to the pump itself.
In an electrical leakage situation, the fish themselves aren't ground so they're fine (although it's still not good for them - think it can cause HLLE ?), but as a person with feet on the ground it's bad.
At least that's how I sort of understand it.
