So I was on vacation for 10 days and came back to find my fry tank covered in algae. So today I scrubbed the tank then did a water change. I noticed these little white things swimming around like snakes. Some are up to a half an inch. I'm not to sure exactly what they are but they seem to be nematodes. How can I get rid of them. And prevent them in my other tank. I have no clue how they got there because I don't have live plants or new fish in the tank. The fry and mother have been in there for almost a month and a half. They only seem to come out when I disturbed the gravel. Are these good or bad and what should I do?