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White worms in the aquarium
I have had an aquarium (70 cm) for 15 years, I set it up newly a year ago. Fish stock: 2 Dwarf Plecos, 10 Cardinal Tetras, 2 Kribensis m/f. My problem: I noticed there are worms in the aquarium. They are white, up to 1 cm long, 1/10 of a mm thin (like a small white thread). They are on the plants, on the aquarium glass (some of them above the water surface). They are partially eaten by the fish. The fish, however, do not die from them (I did not notice any difference). What kind of worms are these, and what can I do against them?
they are rather likely so-called Oligochaetes. The thin diameter compared to the body length and the fact the fish eat them gives hints in this direction. These worms are completely harmless, trying to combat them would cause more harm than benefit. Members of the genus Stylaria are rather common in aquariums. They can easily be recognized by their elegant, snake-like swimming style.
Creeping worms that dwell only on glass panes, leaves etc. are usually Turbellaria, the best known subgroup of which are Planaria. The description in the question, however, does not match them well - Turbellaria have a considerably broader body shape in relation to their body length than Oligochaetes, and they are flat. Furthermore, they are eaten by hardly any fish (some labyrinth fish eat them, but only if they are really hungry).
Turbellaria/Planaria are also harmless towards adult fish, but they may cause total loss of spawn or small fish larvae that are not yet swimming freely (the worms prey on and eat spawn and larvae).
A really effective treatment is difficult, Turbellaria/Planaria and especially their eggs are very resistant. However, you can fairly well diminish their number by siphoning off as many as possible during water changes, by feeding sparingly and by conducting several day food intermissions from time to time, so the fish may reduce the numbers.
Dr. Bodo Schnell