Assuming this is in your DT, the real problem you face now is you have a parasitic isopod (or multiples) on the loose which will continue to attack your fish. I don't have any actual experience with this particular problem, but the info below was gleaned after doing some research. Hopefully there is a better strategy out there than this:
Isopod Parasites (very rare):
Symptoms - These are more frequently seen on shrimp, but some species target fish. They are nocturnal and difficult to distinguish from beneficial amphipods you may have in your aquarium. So, the best way to detect their presence is to watch your fish for evidence of their existence. You will notice bite marks (it’s most evident on any yellow fish), or even the alarming sight of some attached to your fish when the lights first come on. There are even “tongue eating isopods.”
Treatment options - First, remove all fish (except one easy-to-catch yellow fish). The yellow fish will be used as “bait” to draw out and remove the isopods from the fish’s skin (by using tweezers). Rinse & repeat until there is no more evidence of fish-attacking isopods in your tank.