strange creatures in my freshwater tank

Question
I have a 25 gallon tank with a silver dollar tetra and an oscar. The oscar is new since I just lost 3 other fish within the last month or so. I went away on vacation and I got a 6 day feeder upon returning I discovered two dead fish and millions of tiny creatures. they appear to be a whitish color with a very tiny wormlike body. I took a sample to a chain pet store and the Very unexperienced people told me there was nothing in the water and gave me some parasitic tablets just in case. I followed the instructions and they seemed to decrease in number. Then about two days ago there were many many more. They still keep multiplying, my fish seem alright but not really eating as much as usual. I have tried everything and am very frustrated. Please HELP!!
Amanda

Answer
Hi Amanda;

The little worms are harmless planaria or a nematodes. The worms themselves are indeed harmless to your fish, but the cause of their presence is not harmless. They are thriving on excess waste in the gravel from overfeeding, overcrowding  and dirty gravel. Your fish have reduced appetites from the toxic effects of the waste, not from the critters. You have to vacuum the gravel and make water changes to remove the solid waste from the gravel that they are feeding on. Those little critters are very hardy and cannot be killed by medicines or chemicals. Those little buggers even survive bleach treatments! I tried it once many years ago after I moved some fish out of an affected tank.

What you need to do to get rid of them is to starve them out. Cut back on fish food by 1/3 to 1/2. Vacuum the gravel every other day while removing no more than 25% of the water in one day. You might have to do this for a couple of weeks, depending on how clean you can get that gravel. You may see more of them at first because they will get desperate and  will come out of hiding to find more food. They aren't interested in your fish, they only feed on dead decaying waste and food. They will slowly starve out over a period of several days.

Once the critters are gone or greatly reduced, you can avoid further problems in the future by keeping feedings under control and weekly vacuuming of the gravel. You might also consider the type or brand of food you feed. Some have more waste and undigestible fillers in them than others.

Another problen you have there is a tank that is too small for the type of fish you have. Oscars cannot live in a 25 gallon tank. They are far too messy a fish and they get over a foot long. He needs a 55 gallon or larger. He also needs very strong filtration. If you have a power filter that hangs on the back of the tank or a canister that sits outside the tank and connects by hoses, that's great. Get a second filter to help it stay more clean until you are able to get a larger tank. If you have an internal filter, undergravel, box, etc., it is not nearly enough. Get one of the other types I mentioned.

Don't use the vacation feeders anymore. I have seen some ugly results from those things, including dead fish. If you are only going to be gone for 3 to 5 days, your fish are just fine with no food at all. If longer than 5 days, have someone come to feed them for you or get an electric automatic feeder.

I hope things get better soon...

At Your Service;
Chris Robbins