I agree w/ Madding.. I have these worms as well, not sure what they are technically called. I got them I think w/ some driftwood i put in my tank. they seem to be harmless and feed on uneaten food mainly ( seen them now on 'n off for months). I get spikes of these worms when I start feeding more pellets then live food. I think the pellet cloud from the fish chomping them up helps feed these worms.