I dont know that they are a problem but i have tiny thread like worms in my fry tank. I have done a lot of searching and cant find anything like them. Originally i thought they were pieces of lint from my spawning mob as they are super thin and about 3 to 7 mm long. I havent seen them wiggle they are motionless as they float through the water column, the ones on the glass look like they almost have a plunger that comes out the front grabs the glass and pulls the body forward. They appear to be white or grey they are so thin its hard to tell also too thin to tell if they are round our flat, they are literally thinner than a hair. I had been feeding my fry infusoria so I thought they were just some microworm that my fish would eat but they dont eat them. I started to feed the fry boiled egg yolk and now about a week later they are all over the glass and the water column is full of them. Any ideas on what they are would be greatly appreciated. Its a 5 gal
tank with an undergravel filter, 77degrees, ph is about 7, about a dozen zebra danioi fry(almost 3 weeks old) and some java ferns.