Take out your fish put in hospital tank for the time being for a couple days to a week or so. Treat with Mardel Coppersafe it's for internal & external parasites, if needed would highly recommend doing it if a serious outbreak. Best solution boil everything rocks and or sand with occasional stirring the substract, entire filtering system including media sump and or canister, entire tank as far as the tank can hold or brim. Clean from top to bottom & rinse out everything.
I did mine at 97 F + Let it sit with the hot water i mean hot enough to burn your hand not boilng hot for glass. Give it a few hours without adding chemicals like start right ect. DO NOT add cold water to the hot or while galss is hot from touch, will shatter glass or blow out tank depending on glass thickness and how hot the water is.
Let it naturally cool down a few hours before draining out the tank. Basically restarting from scratch. Do the normal refill adding start right with bio extract would be a plus to help get good bacteria back. Add aquarium salt or non iodide table salt. Let it cycle up to 2-3 days before adding your fish back in. Some would consider a week cycle but not needed that long of a time. Also visually checking fish and waste coloration white is bad, gray to black is good.
Now to tell if it worked you will see them floating on top of the water or remain where they last where stuck on glass not moving means they're DOA. I know i said this a few times now, since i had the same problem few days ago myself. It really works in the long run and best treatment. I found this out from a LFS.