Betta Fish Tank Smells Like Rotten Eggs: What To Do?

Can you still call your Betta fish tank beautiful if you must hold your breath whenever you get close to it? No, I guess, especially when it’s smelling like a pile of rotten eggs. But how to get rid of that stinking smell?

It’s possible to reduce the rotten egg smell by changing the water partially. Giving the tank a proper cleaning can also eliminate that smell. Cleaning the filter can also take down the smell if the filter is the source of it. Reducing overfeeding can also help, as it can cause excessive waste production and lead to that smell.

Now the question is, why does it happen in the first place? Well, I’ve found a few reasons so far. Why don’t you check them out by scrolling down a bit?

Key Takeaways

  • Anything like rotten elements, overfeeding, improper water circulation, insufficient filtration, or dirty substrate can trigger a bad smell.
  • It can be fixed by changing the water, cleaning the substrate, removing rotten elements, and improving filtration.
  • The bad odor issue can be prevented with weekly water changes, avoiding sulfur-based water conditioners, and using a carbon filter.
my betta fish tank front view horizontal

Why Does a Betta Fish Tank Smell Like Rotten Eggs?

To fix a problem, you need to know what’s causing the problem, right? Well, the same goes for the rotten egg smell as well. And if I’m not wrong, the smell comes out of your tank for one of the following reasons. 

See also  Should You Breed Betta Fish? [Ethical Considerations]

Rotten Elements

There are a ton of rottable things in your tank, and any of them can trigger that odor you’re hating right now. You never know when a dead fish (or any other creature) is lying there, making the tank smell bad. Even live plants and uneaten foods can do that. So, if you let any of them lie in your tank for too long, be ready to get punched in the nose with the rotten egg smell.


I’ve already told you about uneaten foods, right? Well, this is the most obvious reason for that happening. Excessive, uneaten food can become organic debris that piles up at the tank’s bottom. You know what happens next – hydrogen sulfide, the gas leading to the rotten egg smell we’re talking about.

expert quote betta betta fish need clean water so filtration is essential

Improper Water Circulation

Have you heard about anaerobic bacteria? Well, it’s the bacteria that help in producing hydrogen sulfide and make your tank smell bad. The best place for this bacteria to grow is an aquarium with poor water circulation that creates stagnant areas with low oxygen in the aquarium.

No Water Change

I bet you’ve never seen a Betta fish living place in the wild that comes where they have to stick to the same water for months. So, when you’re doing that by not changing the water, you’re promoting the presence of organic matter and waste buildup in the tank. And once they develop that anaerobic condition, the release of hydrogen sulfide is just a matter of time.

Insufficient Filtration

Do you know the most effective way to remove organic waste and debris from your tank without breaking a sweat? Installing a good filtration system. Now, imagine having a defective filtration system. Not only will that mess with water health, but it will also make the tank a source of an irritating smell.

Keeping It Dirty

Bad odor – isn’t what comes next to anything that you keep dirty for a long time? Well, the Betta fish tank is no exception here. The longer you leave the accumulated waste there, the more it will stink. 

See also  Betta Fish Care Tips for Beginners: Expert Advice from Mary McCauley

How to Fix the Rotten Egg Smell Issue?

Okay, if that’s the smell hitting your nose, something seriously wrong with your tank, such as a rise in hydrogen sulfide gas. So, to fix that up, let’s start with –

Testing the Water

Check the water condition of your tank with a water testing kit. Yes, I’m talking about the parameters, especially pH, ammonia, nitrate, and of course, temperature. If the water is smelling too bad, try improving these parameters first.

Water Change

Hold on a second! Nobody said that you need to fill up the entire tank with new water. To lower the odor, replacing 20% to 30% of the water with dechlorinated water should be enough. But make sure you’re keeping the temperature the same as the previous water, as it helps dilute the toxins and improves the water quality.

Cleaning the Substrate

This is where all wastes and organic matter pile up and decompose. So, when it comes to cleaning, this is the first thing you need to clean up. Try using a gravel vacuum for a thorough cleaning.

my betta top view

Removing Rotten Elements

It’s not always the fish poop that makes your tank smell like rotten eggs. Check your tank to see if any decaying matter or dead plants are lying around. Get rid of them instantly, as they can boost hydrogen sulfide production and make your tank stinking. 

Improving Aeration and Filtration

Proper oxygenation can keep foul odors away from your tank. But for that, you need to ensure proper aeration first, as that will prevent any anaerobic conditions. Plus, you must ensure the filter is not jammed with clogs or buildup. If you can trace anything like that, clean the filter media and replace it if needed.

See also  Why Did My Betta Fish Change Color From Blue To Red?

Stop Overfeeding

As a Betta fish owner, you must know how much your fish can take. So, make sure you’re skipping overfeeding in every possible way, as that will pile organic matter in your tank and make it stink. And if you see any uneaten food in there while cleaning, get rid of it.

expert quote betta nowadays i like to use a sponge filter just because it's already really gentle make sure you do regularly clean it maybe like once a month

How to Prevent the Tank from Stinking?

If you can get this part done, I don’t think you’ll have to worry about the rotten egg smell ever. All you have to do is follow these tips.

  • Change the water weekly, at least 15% of it. If your tank is filled with fish, make the amount 20-30%
  • Remove all the uneaten food as soon as you see them, and don’t overfeed.
  • Check the tank weekly for rotten elements. Keep the count of the fish so that you don’t fail to find a dead fish.
  • Clean the tank regularly, including its decor, rocks, and gravel.
  • Avoid water conditioners with higher amounts of sulfur.
  • Remove any dying plants from the tank. Check if the leaves are turning yellow or brown.
  • Use a carbon filter, as that can eliminate bad odors.
  • Don’t overstock the tank with fish.

Before We Go…..

Clearly, you need to clean up your tank if the smell is going over the top. If you’re a beginner with no experience in tank maintenance, I guess you’ll think of using some soap in the process.

Hold it right there! Before you make a move, check out my blog – Can You Clean A Betta Fish Tank With Soap? You need to see this before putting any soap in your tank.

Sharing is caring!

Muntaseer Rahman

About Author

Hello, I’m Muntaseer Rahman, the owner of I’m passionate about aquarium pets like shrimps, snails, crabs, and crayfish. I’ve created this website to share my expertise and help you provide better care for these amazing pets.


This site is owned and operated by Muntaseer Rahman. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to This site also participates in other affiliate programs and is compensated for referring traffic and business to these companies.