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Worms in media


AC Members
I have a 20 gal tank with 4 fish and about a dozen snales of 4 types, several types of plants and a stock 20gal filter system. I used plant medium mostly, it’s about 1.5-2” deep in most parts. The tank has been running about 6 month just fine.

Till about a month ago these worms weren’t around. They are thin like paper, light brown I guess, they vary in length from 1/2”-1.5” out of the media but go in to the media I’m not sure how far, they are fast , they retract in to the media any time a fish or snale touches them. They do not seem harmful but my water has been more and more yellowish in tint over the last month and now there are thousands of these things waving around at the bottom of my tank.

Thanks for any info 165D1245-D3FD-4E96-8C84-DDCA1F23F3F0.jpeg5498E071-6F61-46E4-97A4-8A1B89F593BF.jpeg


No freelancing!
Black worms. They are often sold as a live food source, but they will happily live in the substrate. They aren't related to the change in color, that's more likely to be from tannins out of the wood. Harmless, though some don't like them. Sorry if adding a fish to eat them, I don't know how to eradicate them, but feeding less and cleaning more will reduce numbers significantly. What fish are in there?


AC Members
I have 2 large fancy goldfish , one medium pom pom goldfish and one that umm I’m not sure about . It looks like a stream trout but only 2 inches long, it had a companion but it died I think to age , they came in from an outdoor pond I have other goldfish in .

The large fancy are like softball and baseball size comparatively, the pom pom is like a golf ball, each ball with fins sticking out of them. So I have a 50gal tank I’m getting.

What eats these?
Should I allow them in the 50gal tank?
How big do they get?

Thanks for the infos BDD492E2-3FBD-45A5-95D6-3F9EECBF5FFB.jpeg


AC Members
Blackworms are an OK addition to your tank IMO. They can be a food source for your fish, if they eat them. They also live off some of the "detritus" as part of the circle of life in our tanks. No sweat!... Unless they suddenly die off & pollute the heck out of your tank

the loach

AC Members
Surprised the goldfish don't eat them. But then, your substrate isn't ideal; much too big for them to go through. You wouldn't have that much or even at all with small gravel. Great pics Btw.


AC Members
Thanks, I was thinking to use more smaller media and some sand areas in the new tank build.

All the fish clean the larger media bits, I suspect that’s for algae tho, is there any fish that like them or are fast enough to pluck them?

Thanks for the infos

Pickles says thanks 21D98A54-52FB-483A-A83E-15540D08D88B.jpeg


Eheim User
I would find it odd if they were black worms IF you never added them to your aquarium.

I also did not see any mention of driftwood in your tank.

How often do you do water changes on this tank and how much water do you change when you do?


AC Members
I do not have any wood in my tank , it is plant medium however, it is rocks some silt and some nutrients for my plants.

I have not added any live food to my tank other than snales.

I have brought fish in from outside but that was months ago now.

I water change every week to two weeks depending on water clarity, I normally do about a 30%change that I mix my salts and conditioners in , in total just over 6-7 gals each time , changing filters every month depending on how messy the fish have been.

Looking at google pictures Black worms, I did find a pic that was similar to my worms but so many other “black worm” pictures came befor that I’m still not sure about them also.

Thanks for the info’s


Global Moderator
Staff member
Chron, welcome!

What are your nitrate readings in PPM? Given the size of the tank and the bio load you have in there, a 15gal water change once per week probably wont keep nitrates to a healthy level. You'd need to change more water than that. Clear looking water does not mean healthy water. Like said, worms may have come in with a plant or decor and are living off the waste products in the substrate.