Ewww.
Sorry
LOL I just hate things that crawl like that. Most likely caused by overfeeding. I grabbed this from
http://userpages.umbc.edu/~rrhudy1/micro.htm :
"Planaria:
If small white creatures are seen crawling all over the glass and ornaments, especially at night, they may be planaria. Planaria commonly show up in tanks with an excess of food. Most are introduced to an aquarium from other aquaria with live foods like black worms, live plants, or anything else moved from an active aquarium that has them. There is some belief that they can survive in freeze-dried or frozen foods. If a lot of food is left in a tank; including dead and dying fish, snails, other animals, and plants; then a few planaria may divide into hundreds very quickly. They usually reproduce by asexual fission. Their heads are shaped like arrow heads. If a tank is found to be infested, planaria can be controlled by a good vacuuming of the gravel and better tank maintenance. To remove more planaria, see the next section on controlling planaria. Planaria will eat dead fish, fish eggs, and immobile fish larvae (fry newly hatched). They do not pose any risk to mobile fry or adult fish.
Controlling planaria in aquaria:
1. Set out bait like meat in a mesh bag. Remove the bait a few hours after the lights go out on the tank. It should be covered with planaria. Throw away and repeat until the population goes down.
2. Add planaria eating fish to the tank. One species is the paradise fish.
3. Vacuum the gravel very well and do a 50% water change. Often, planaria proliferate when the tank is too dirty. This will remove not only some planaria but their food source as well.
4. Reduce the foods added to the tank. Planaria often proliferate if too much excess food is provided.
5. As a last resource, tear down the tank. See here for information on tearing down tanks."
Personally I've never dealt with planaria, but I did have a nematode infestation (same idea, diff species). My clown loaches found them delectable and decimated the population once they discovered them (and watching them get nose down in the substrate and wiggle their butts to get to the worms was hilarious!).
