I'd get the praziquantel ready, Joel. Here's some info on how prazi can be dosed.
Remove carbon.
Add 2.5 milligrams per liter of water.
If you are using the powdered version, it is difficult to dissolve. Predissolve in tank water by shaking it up in a small container.
Dosing
Day 1 -- remove carbon, perform water change with vacuuming, and add Prazi to tank
Day 2 -- add Prazi
Day 3 -- do nothing
Day 4 -- do nothing
Day 5 -- do nothing
Day 6 -- add Prazi
Day 7 -- add Prazi
Day 8 -- normal partial water change with vacuuming
Day 14 - normal partial water change, then add prazi
Day 21 - normal partial water change, then add prazi
Day 28 - normal partial water change, then add prazi
Day 35 - normal partial water change, add carbon, treatment is complete
Are you sure that's not even a slime coating?