Is dropping a bromine tab in my sump pit bad?
It won't mess up your pump, there's much heavier minerals in the water than bromine. However, you have to be weary of where the water is discharged. Bromine isn't going to be healthy for your lawn or nearby trees. It's probably best to spot-treat the mold with bleach and maybe mold-resistant epoxy paint. If you use bromine, re-route your discharge into the sewer.