My filter went out and I was gone all day. I got home aroung midnight and noticed this and plugged the filter back in and saw how a whole bunch of what looked like white "fibers" infiltrate the water! Then I noticed these fibers were moving!!!!! What can these be that were living in the filter??? Are they harmful to the fish???? The fish seem freaked out by them and are in the corner of the tank! HELP!!!!!!!!!!!

Hmm, they could be oligochaetes (related to earth worms). They are scavengers and feed on the fish wastes in the gravel and the filter. Maybe the sudden surge of water through the emptied filter washed some of them out. They are harmless, BTW.

However, if they are flatworms then it is not so good as they can be a problem for the fish.

Are they still floating around? Can you describe them better?

Sounds to me like its just some kind of poo-eating worms that have been growing in the filter (and in the gravel). Icant remember what they are called right now but the best way to combat these worms is to do very thorough gravel vacs and keep your filter flowing freely. you wont be able to totally eradicate them, but there will be a lot less of them around. And i agree, they are totally harmless.

I forgot to add that 95% of the worms you can visibly see in a freshwater aquarium are completely harmless but they do signify a lack of cleaning and/or overfeeding.

paul

That;s what happening in y fish tank. They're like string-like white worms and they are moving around my tank. My fish aren't as active as usual. One of my fish had body fungus, it seems to be disappearing though. I haven't medicated her yet. I thought these white things were responsible. You say they won't harm the fish, but I have a batch of new fry in my tank. (They have their own unit in there.) Would these things hurt them? Should I medicate my fish with the body fungus even though it's disappearing? If I did medicate her (the tank just in case the other fish might have caught it) Would my fry be affected by the medicine since they are a little young?