Worms/Flies In Tank

Question
About a couple months ago I noticed a small kind of stubby looking fly whoosh out of the tank when I opened it, I did not pay any mind to it until I saw about 2 more on the glass on the inside of the tank and then I noticed little black/gray worms crawling on the glass inside the tank. I have a goldfish and a Pleco and I thought it was the algae tablets we were using because that is the only change we did before the flies and worms appeared. I noticed on this forum about flatworms and nematodes, but I looked at the pictures and both of them look nothing like what we have, so I am not sure what we have a how to fix it. We have no gravel in the tank either. Any information you could give would be greatly appreciated. Thank You!!

Answer
Stephanie,
It could be Plananria which are worms that some out when fish are being over fed and the water is not being change often enough. They are relatively harmless to your fish, you will want to get rid of them so they do not take over your tank. To do this, feed your fish once a day, and only what they can eat in 1-2 minutes, and then remove any uneaten food from the tank. Goldfish are very messy fish and can contaminate the tank very quickly. Make sure that they are in the right size tank and that the filter is for a larger one. Weekly water changes will also help prevent worms in the tank. With the goldfish, it is good to remove 25-50% of the water weekly, replacing it with clean conditioned water. Once all this has been achieved, you should start to see the worm population decreasing.