Tank has little white squirmy worms

Question
Hi Chris,

I have a 100 gal fresh h2o tank I purchased used. It uses a wet dry filtration system instead of the filters that use carbon. I started noticing these little white squirmy worms in the morning when I turn on the light then some types of my fish love to eat them. I guess they can't see them when it's dark but as soon as I turn on the light and the fish wake up they go to town eating these worms, there are hundreds of them. Some are really small but some are almost 1 inch long. I'm worried they maybe harmful to my fish because everyday for the last 10 days a fish would be dead floating at the top of the tank. I also noticed most of my fish use the sandy bottom to roll and scratch themselves on. Do you know anything about these worms? Someone at the pet store said they come from the filter and live off the good bacteria and if I use Coppersafe to kill the worms it will also kill the good bacteria.

I also noticed the Zebra fish have gained a lot of weight over the last week.

I'd appreciate any help / advice you can give me.

Best regards
Rich

Answer
Hi Rich;

They are just harmless nematodes or planarians that are feeding on excess organic wastes. They do come out more at night and many fish do like to eat them, which is very healthy. The planarians themselves are not harmful to your fish but the reason that they are so plentiful is very harmful; Overfeeding. They are a symptom and the over feeding is probably the cause of dead fish too.

The little critters can't be killed with chemicals or medicines. It would be devastating if it did anyway. Along with excess waste already there, now would be hundreds of those dead bodies in there making more pollution too. They are very strong and resilient little fellas. The only effective way to get rid of them is to starve them out by cleaning the gravel and cutting back on how much food you feed the fish. It will take some time and effort but unless the cause of the infestation is handled, you will probably lose more fish and the planarians will keep reproducing.

Start by cutting back on food by 50%. Your fish only need enough food once per day that they can consume all of it from all areas of the tank in 5 minutes or less. If there is food leftover after 5 minutes, it's just providing nutrients for the worms and polluting the tank. Even if your fish eat it all after a longer period of time, they can't digest it efficiently so too much waste is produced. It all goes into your gravel for the planariana/nematodes to thrive on. Right now until the problem is under control it's okay if it takes much less time for the fish to eat. You will want them a bit hungry right now so they will eat up the excess worms.

The next step is to make a series of gravel vacuumings and partial water changes. What you want to avoid is draining the tank and "cleaning everything out". It will cause serious stress to your fish and can kill off all the beneficial bacteria that is already struggling to consume the excess waste. Remove 25% of the water every couple of days while vacuuming the gravel. All tanks need a weekly 25% change and gravel vac every week but yours needs it more often for awhile. Do this until there is very little crud coming up in the gravel vac tube. It may take a week or two but it really is necessary. Move rocks and decorations to get at any really nasty spots. That stuff is becoming toxic down there. If you don't already have one, shop for a "spill-free" water changing system at your local fish store. It is a gravel vac with a very long hose that attaches to your faucet with a special pump. It drains and refills. You don't have to haul buckets and works GREAT. I have used them for years.  

Let me know how it's going...

At Your Service;
Chris Robbins