hi i am new here.we have about a 15 gallon freshwater tank with five freshwater tropical fish and 3 ghost shrimps in it.we sometimes use a little stress coat and occasionally a good bacteria supplement.everything looks ok except today my daughter and fianc'ee claim to have seen a white worm in the tank.they said it's about an inch long and looks like a piece of string.so far i cannot see it since i got home.they said it maybe went under the rocks.has anyone ever heard of this type of thing?thanks