Thsi is from a betta website but it might help you with your fish.
DISEASE: EXTERNAL PARASITES
GENERAL INFO: If you do not add some aquarium salt (1 teaspoon per 5 gal) to your betta’s water, your betta is likely to get some parasites. Especially if you feed him live food, or worse yet, frozen live food, such as frozen brine shrimp. These frozen food carry a lot of parasite eggs I guess, because the correlation between frozen live food and the onset of a parasite epidemic has been well established both by me and other breeder friends of mine.
SYMPTOMS: It is easy to diagnose a betta with external parasites:
It will dart and scratch itself against anything it can find, such as gravel, rocks, heaters, tank walls, etc… You will probably never be able to actually see the parasites themselves. Look instead for a behavioral change in your betta. If it looks like it is on speed or acid, then it has parasites!!

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TREATMENT: Do a full water change for jars or a 70% water change for tanks. (To get rid of some of the parasites and their eggs, etc..). Easy and efficient, immediately add AQUARIUM salt (1 tablespoon per 5 gallons) (and NOT table salt, duh!!) and add one drop of aquarisol per gal. I personally recommend always adding the above to your water to prevent any parasites. I NEVER have ANY, because I religiously add both salt and aquarisol to my water. If the epidemic is advanced, you might want to go for something a little stronger, like “Clout”. Clout will color your rocks and the silicon of your glass tank blue

. A small price to pay to save your bettas, though… Follow manufacturer’s directions.