I have these little worms (some 1/2 cm, others are 1-3 cm long) in my 10 gallon tank(which doesn't have any fish in it yet). I first noticed them when I replaced my gravel with sand (estes marine sand.) Then I switched the sand with gravel, because the sand jammed my whisper filter. So I guess the worms were staying alive in the filter, because I ended up fixing the filter. Then when I ran the filter on my 10 gallon, about 20 worms just came out with the water and are swimming in my water. Now I think some got sucked up by the filter and I only noticed about 5-6 when I checked on my tank last. The worms are not very thick, they look like white strands of hair. So my question is, are these worms harmful at all, will they reproduce and be annoying, or is it just normal?