If its fish lice, Anchors away or any medication with dimilin. ( Diflubenzuron is another name for dimilin)
There is another medication from Tetra called Parasite guard which is a shot gun parasite med that contains four different meds that is rays safe by my experience.
Key with parasites is treating long enough. Treat for one cycle then break and treat again in a week to kill off any potential new hatches. I personally would do this on multiple cycles over a period of 30 days to be safe giving a break in between cycles.