I believe these are a type of nemotodes as no-planaria/fenbendazole does not kill them. I have had these in my tank as well at one point, and I also dosed fenbendazole. Didn't work either. I just sucked a few out a day with a fine tipped syringe. The population eventually just went away.
Hmmm. The only thing I have in the tank are Oto's and plants. Tossed in an algae wafer before a 4 day trip and came back to this mess.
Have been planning to add a school of habrosus, but thought I'd wait until the outbreak cleared. Should I instead add the fish and hope they clear the outbreak, or is there something else I might try before adding fish. I'd rather not wait for them to go away on their own!