Worms in tank

[Amaray]

I recently got a tank and was given some used gravel. I rinsed with hot water and put them in a tank planning to cycle before I bought any fish for it. Hours after I filled the tank I saw many small black worms swimming around the top of the tank, as well as some that were sinking to the bottom. What could they be, and are they harmful to any potential fish I add?

 

[EllieTheJellyy]

You should never put anything that has been used in your fish tank in my opinion, they could carry diseases. These look to be non-parasitic worms as they are fairly visible, but you should remove them just in case. They’re like snails so they’ll feed of fish food and are nocturnal but they’ll also breed so unless you want your aquarium to be full of these best to replace the gravel and clean the tank out again or you can set a trap by using a non see through jar and put some bait in it like fish food.

 

[Colin_T]

Hi and welcome to the forum

Any chance you can take a picture showing the worms from the side rather than above?

 

[The Lumpfish Guy]

You should never put anything that has been used in your fish tank in my opinion, they could carry diseases.

Most aquatic organisms have little tolerance to UV light, keeping spare nets, heaters and other equipment dry and in the sun will remove most bacteria. A good clean after the last use (just hot-to-boiling water) will see off the rest. Gravel ect is still probably OK provided that you clean it before again just hot-to-boiling water will kill off most unwanted organisms.

If people are really fussy about contamination, using a un-fragranced bleach ( should just be a solution of Sodium hyperchlorate) can be used to disinfect nets, heaters and equipment after tanks have been closed down. Obviously rinsing after this has been done, but the active ingredient will deteriorate over time. Milton fluid ( if your are in the UK) is a similar sort of thing but with added salt.