Tiny thread-like swimmers - what are they?

[stine]

We recently re-set up an old 30 gallon in my son's room. We reused the gravel and filter sponge from the established tank, but it was due for a good cleaning and added new water aside from that. Today we are seeing little linear creatures wiggling and darting around. They are very small and at first I thought they were just debris. Assuming they are alive, which they do appear to be as they "swim", what could they be? Would they be harmful to freshwater fish we may add?

Thank you!!

 

[Andrew McFadden]

Are they white or clear like a very small worm? If yes then
It's called planaria and to get rid of it do regular water changes and feed less. Also cleaning the filters may be needed. Planeria usually come from poor water conditions. Too much food left over, etc. Water changes will remove them. Also fed less. Make sure to wash you filters material in tank water not tap water. The worms wont harm you.

 

[stine]

Thanks for the reply. They are colorless, or at least not a distinct color. They whip their tails around when they swim. My concern is the gravel and filter sponge were taken from an "abandoned tank". Our old giant pleco died several weeks ago, he was the last fish in there before we did the tank move yesterday. Now I wonder if these worms could have harmed the pleco? I am hoping they are just incidental. My son is of course anxious to add fish when the tank is cycled, but I want to know the deal with these uninvited guests first.

 

[Andrew McFadden]

Thanks for the reply. They are colorless, or at least not a distinct color. They whip their tails around when they swim. My concern is the gravel and filter sponge were taken from an "abandoned tank". Our old giant pleco died several weeks ago, he was the last fish in there before we did the tank move yesterday. Now I wonder if these worms could have harmed the pleco? I am hoping they are just incidental. My son is of course anxious to add fish when the tank is cycled, but I want to know the deal with these uninvited guests first.

If they are what I'm talking about they can't harm you or the fish. Oh and to AA I thought I put that on the last post