On the tank glass? These are normally present in dirty tanks with left over food in the gravel etc, feed less or wc more. If they are on the fish, it's some type of parasite and should be treated as such.
got the same problem just saw it today so freakin me out,,will do water change 50% and what else that we can do to kill it but not kill the fish coz i know sometime if use medication will effect the fish ,,thank you
Clean your filters, do a gravel vac, keep up with maintenance (water changes, filter cleanings), and feed less! Detrus worms (small squigly worms that look like and swim like a sperm tail) are harmless and are a sign of too much organics in the water and grossly overfeeding. They aren't harmful and actually are helping by feeding on all the built up organics in your system. Actually good for feeding smaller fishes...