tiny white worms

Question
We have a 55 gallon tank that has been set up for 4 years, and we still have fish in it from when we set it up of course we have added to it. We have 8 fish: 1 black tetra skirt, 2 bala sharks, 2 african leaf fish, 2 guaromis, 1 plecostomus. We use a carbon filter cartridge with amonia chips. pH is between 6.5 and 7.5, there is no ammonia or nitrite. We change the water about every 3 weeks, and we change about 25%. We just noticed today at the top of the water tiny white wiggling worms. What are they and where are they coming from, we recently bought 3 bottom feeder fish one at a time that have died within weeks of having them. Are these worms causing the death of our bottom feeders?  

Answer
Hi Micah;

The worms are not harmful at all, but the cause of their proliferation in your tank is dangerous. They are a type of planarian or nematode and are totally harmless to your fish.  Planarians feed on excess waste in the gravel and some will crawl to the top where excess waste sticks to the glass just above the water. The excess waste is why the bottom feeders died too. There is just too much crud down there. Overfeeding and lack of gravel vacuuming are the usual suspects.

You need to get the gravel bed back in shape so it will support bottom feeders again. You will have to perform a series of gravel vacuumings and water changes in order to clean the gravel and it will consequently starve the little critters out. There is no medication or chemical that will kill the planarians without killing the fish, and they aren't harmful so you don't need to do that anyway. Before I knew what they were years ago, I even took the fish out and tried bleach. The little suckers survived! Strong and hardy guys. The only thing they can't tolerate is starvation. So, cut back on food and clean, clean, clean! Just don't do too much at once. It must be gradual.

Every tank really needs a weekly 25% water change (EVERY week) and a gravel vacuuming at least every two weeks. To get things back in shape, do a gravel vac and 25% water change together twice a week until you aren't getting much crud out of the gravel anymore. It could take 2 or 3 weeks but it's worth it. Unless it's REALLY bad, avoid the urge to empty the tank and "start over". It would shock your fish and they may not survive such a trauma as the tank goes through a break-in period again as it did when new.

You may see more worms at first, but that's normal. As the gravel gets cleaner, they will come out of their hiding places to find more food so you see them more easily. They will starve and slowly disappear.

I hope all goes well...

At Your Service;
Chris Robbins