Is there anything that eats aquarium fish waste?

Yes, there is! The best fish waste eater out there is a siphon hose! :)

Obviously others are completely correct, there is no animal you can put in the tank to eat the waste.

I'm not sure about waste, but if you get a snail it will eat the algae from the walls and bottom of your fish tank.
Nope No animal for fresh water eats fish waste.
large thriving colonies of java fern and frogbit would do the job. Its not as simple as throwing the plants in the tank & having it do the job... It has to be a healthy thriving community of plants with bubbles rolling off of the leaves, which takes a lot of equipment to do correctly.

There are some pages out there that detail household (non-aquatic) plants that you can dip in the water to suck nitrates & the like out of the water. Ditto for the plant health though. They have to be in sunlight & growing for it to work.

Really, its easiest to just do your water changes & carbon changes regularly. If you screw up the plants, its worse than not having them.
If you mean the uneaten food at the bottom you could get some Cories, Plecos, or Chinese Algae Eaters, snails and a good filter. Also a well planted/well lit tank will utilize the wastes for growth.
Unfortuneately no, you can get algae eating fish that eat the algae, snails do too, but the only thing that gets rid of fish waste is a gravel syphon hose-sadly!. Hope this helps. x
I'm not quite sure if this is the technical name for it but my family had a "sucker fish" in our tank when I was little. It looks like a teeny tiny baby shark and it just attaches itself to the tank and hangs on by it's mouth. You will never see this fish anywhere but on the glass. lol. Just go in to a pet store and ask them about it they should be able to tell you what the fish's real name is and possibly find a better cleaning fish for you. Do not get snails though. They multiply faster than rabbits!
Biological media eat fish waste. It takes a few weeks to start building up enough bacteria to control your aquarium environment.

If your aquarium is under-filter(does not have enough filtration), you can add biological filtration by using large rocks in your aquarium. The fish will love hiding in them, too!

Also, you will need to get one of those suction cleaners from Walmart or a pet store and suck some of the junk out of your gravel at least once a month. Just suck it into a bucket and refill with fresh water. It does not take long and it will keep your fish happy and healthy.
Keep in mind food = nitrates. It doesn't matter if something eat the food, if it rots, or something eats the fish waste. You end up with ammonia, which bacteria convert to nitrite, which other bacteria convert to nitrates. Plant will absorb it, but you'd need roughly 10-30 the mass of healthy growing plants to deal with the nitrate. Also you'd need to remove any dead leaves, and such.

Basically the answer is no.
snails but they grow out of control
no but plants love it if you siphon it out then give it to house plants
yes there is I think if you look in any of your local pet stores there could be snails and differnt kinds of catfishes.
There are some things liek shrimp that will pick at the undigested nutrients in fish poo, but remember that anythign that eats will also poop...
Check out a product called Biozyme (versions for freshwater and saltwater aquariums).

From the link article below:

"Biozyme is a living system of beneficial bacteria in concentrated form, which is activated upon introduction to water to convert lethal ammonia and nitrite to less harmful nitrate. It quickly reduces fish wastes to inert substances and breaks down organic buildup in gravel beds."

This isn't a substitute for regular aquarium maintenance like regular water changes or under gravel siphoning but it certainly helps reduce the frequency. I've used both the fresh and saltwater versions in my tanks and haven't had any nitrite or ammonia issues since I got into the hobby back in the late 80's.

Biozyme is available at most aquarium shops.
A gravel vacuum.

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