they are some sort of parasite (as im sure u guessed) i was gunna say planaria but ive never heard of it on fish, do a 50% water change, add aquarium salt and melafix and d 20% water changes daily for a week or so.
Look at the product called Had-A-Snail
see if it will work for you...
I had nematoads and another parasite living in my tank that i got when i transfered some rock from a friends tank...
One made the fish scratch, tiny little things crawling all around them... the other looked like a tiny transparent little thicker then hair eel on speed...
used had a snail in the AM and by the PM all was good... let it sit for 3 days then did a 50% water change... I hit it again as i was advised and let it sit another 3 days then did another 50% water change.. 3 days later another 50%... 2 weeks now and no sign of parasites...
i would keep up with the waterchanges, salt and i would get a medication specifically for parasites. also syphoning the gravel really well for a while to pick up the cysts will help.
