i was doing my routine cleaning of the gravel and saw some baby fry in the tank so i started to suck them out of the bad bucket water and into a fry tank when i noticed some nasty looking white things all over in the water. they are shaped like leeches but the biggest one i see is only 2-3 mm long they are gross. can anyone tell me what they are and how to get rid of them without killing my fry?