There are parasites in my tank with my oscar.

Question
For Valentines Day I feed my oscar 3 goldfish for a local pet store. About a month ago I noticed 3 spots on my gold oscar.  The biggest one was maybe a 1/2 in diameter.  First they turned gray, then black, then white and now there gray again.  I thought that it was fungus so I treated with Melafix and pimafix. (not at the same time)  Last night I noticed little bitty probably a 1/8 of an inch white worm looking things crawling on the inside of her 55 gallon tank.  I just did a 30 gallon water change sunday and the tank was perfect.  The parasites don't look like there growning on her though.  Please help me.  In the tank there is also a zebra stripped catfish and a brisstle nosed plecko.  They all have been living together for about 5 years.  In the tank I have 2 powerheads with an undergravel filter and a filter that hangs of the back of the tank with 2 carbon filters in it.  The PH is up to 7.5.  I don't know what to do.  

Answer
Hi Stephanie;

These are a type of planaria and are totally harmless to your fish. They do indicate excess waste due to overfeeding. They live in the gravel where they feed and you can't see most of them. We all overfeed from time to time, we just have to learn when to realize it and clean up after ourselves when we do.

There is no medication, treatment or chemical that will get rid of them. You have to starve them out with a series of gravel vacuumings and cutting back on how much food you feed.  Vacuum the gravel every day if you can for a few days, removing no more than 25% of the water at one time. This will get the gravel clean without stressing the fish out too much. You will start to see the planaria die out over the next two weeks or so. At first, they may seem to be increasing in population, but this is simply their reaction to starvation. They are seeking more waste to feed on, coming out of their hiding places so you can now see them.

The spots that were on your oscar are not related to the planaria, but may be related to the overfeeding. Once everything is cleaned up and kept that way you probably won't see that again either.

Followups welcome

At Your Service;
Chris Robbins