bug or parasite in my tank

Question
i have a 55 gallong tank i have had it for years but here lately we have had some bugs or parasites come up in the tank there like little white maggots about 1/2 or less inches long then they mature into a fly type creatue and the main place we find then is in the filters when we take the covers off the filters there on the sub filters the fly things and the worms all i have in my tank is a alge eater  4 crayfish  and 6 goldfish

Answer
Hi Adam;

They are just harmless pond creatures. They feed on the waste your fish make. Annoying, but harmless.

The part that is not so harmless is the reason the little critters are thriving. They are feeding on waste. Goldfish get big and messy so there may be too much waste in the system. Be sure to make a 25% water change and vacuum the gravel weekly to help keep it under control. Even twice a week is not too much in that size tank with that many goldfish. Avoid overfeeding too. It's a pretty common problem with goldfish. I enjoy my goldfish too but they are gluttons by nature and in return just create more waste than most other fish do.

At Your Service;
Chris Robbins