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Your Fish Tank Smells Bad? This Is What Your Aquarium Water Should Smell Like

6 min read

There’s no doubt that aquariums are a pretty sight, but what about the smell? What should your fish tank smell like?

Your guests may be enthralled by your fish tank and may want to take a closer look – if the fish tank water smells bad, they will promptly take a few steps back. You wouldn’t want that to happen, would you?

No, your aquarium should be pleasing to all the senses. Not just that, a bad smell from fish tank might indicate that something is off and your fish could be in danger.

Let’s find out what healthy aquarium water should smell like and the reasons why your fish tank smells bad. Also, we’ll look at how to get rid of fish tank smell. 

What Your Aquarium Water Should Smell Like

So, you are wondering whether your tank smells all right, or it’s not and something is amiss.

There should be no noticeable smell from a healthy aquarium when you are standing next to it. If you pick up a strong odor, then something is out of order.

If your aquarium smells lightly organic or earthly when you put your nose right next to it, it’s absolutely nothing to worry about – most aquarists report the same smell, so that is what a normal tank should smell like.

You wouldn’t even notice that smell if the aquarium is closed-top and you’re standing a bit away from it.

On the other hand, if you notice any strong odors from the aquarium water, then something is definitely wrong – it could be one of many things.

Why Does My Fish Tank Smell Bad?

Fish tank with protein foam

If your fish tank smells bad, there could be various causes – you can figure it out by identifying what is it that you are smelling exactly.

One of the main reasons for your aquarium to smell bad is the decomposition of organic waste. Decomposition is a natural process where bacteria break down organic matter. 

If you go by experience, decomposition is not pleasant to your sense of smell at all. It releases ammonia and sulfate compounds, which have distinct pungent odors.

Dead fish can decompose and release a bad odor – see if any of your pets is missing. Dying plants can also smell bad, although not as bad as a fish corpse. 

If you overfeed your fish, the excess food will remain in the tank and eventually become food for bacteria. Even fish droppings are fair game to bacteria. 

Too much organic waste can lead to protein foam on the surface of your water; in addition to smelling bad, protein foam is not a great look for your aquarium.

If your aquarium smells fishy (no pun intended), it could be due to ammonia. Many describe the smell of ammonia as akin to pee or sweat – very undesirable, as you can imagine. 

Worse still, ammonia is toxic to fish and can kill them, so you should be alarmed if you smell it. A properly cycled tank should not have any ammonia in it. If you do detect ammonia, you should change the water immediately and find out what’s releasing it.

If your fish tank water smells like pool water, it could indicate high chlorine levels. Like ammonia, chlorine is toxic to fish and should be dealt with immediately. 

Tap water usually contains chlorine; if you use tap water to fill your aquarium, make sure you use a dechlorinator to get rid of the chlorine so your fish can be safe.

Why Does My Fish Tank Smell Like Rotten Eggs?

This is one of the worst smells you can have in your aquarium. If your fish tank smells like sulfur, it is due to hydrogen sulfide, which is a toxic gas released when bacteria decompose organic matter.

Hydrogen sulfide is more likely to be released when there are anaerobic conditions in your tank; there could be spots in your tank with poor flow and insufficient oxygen.

Moreover, pockets of this gas can build up within the substrate where oxygen is not prevalent; when disturbed, this gas will be released, causing the unpleasant odor.

If your aquarium smells like sulfur right after you have used a dechlorinator then don’t worry: some dechlorinators have sulfur in them. It should dissipate after a while.

How To Get Rid Of Aquarium Smell

Once you detect any offending odor from the fish tank, it’s time to spring into action. 

You can get rid of any unsavory smells by eliminating the cause of that smell. Use the following methods to get rid of fish tank smell. 

  1. Clean the Tank and Filter

If the bad smell from fish tank is caused by excess organic waste, then cleaning the tank should be your go-to option.

If there is any dead fish, remove it immediately. If parts of your plants are turning to mush, then trim them accordingly.

Uneaten fish food and feces will settle to the bottom – make sure you clean them by using a gravel vacuum.

Don’t forget to clean your filter! Your filter collects all waste, so it gets dirty the fastest. A clogged filter will also lose efficiency, leading to a dirty tank.

  • Change the Water

If you suspect ammonia or chlorine in the water, you should change the water immediately, as these are toxic to your fish. 

You would be doing regular water changes anyway as part of your aquarium maintenance, but you may have to do a one-off if you detect any harmful chemicals.

Make sure the water you replace your tank with is suitable for aquariums – tap water won’t do as it contains chlorine.

Be careful though – changing the water may only act as a band-aid as long as the underlying condition remains unchanged.

  • Use Activated Carbon

Activated carbon is widely used – not just in aquariums – to get rid of unpleasant odors. The carbon absorbs odor-causing molecules onto its surface.

More than that, activated carbon also absorbs toxic chemicals such as chlorine and chloramine. They also remove tannins, which make the water yellow.  

Use an activated carbon media in your filter to reap the benefits of it; the carbon media should be placed after the mechanical filtration for it to be effective. Also, you should change it periodically as it loses effectiveness after absorbing various chemicals. 

  • Ensure Proper Aeration and Water Circulation

As we’ve seen, anaerobic bacteria can generate hydrogen sulfide in areas with insufficient oxygen, leading to the unpleasant smell of rotten eggs. 

You can prevent this from happening by properly aerating your tank and improving water circulation – more air pumps may help, or you could use a stronger powerhead for your filter. Placement of these components is also important. 

Proper water circulation also ensures that organic waste is efficiently collected by the filter so that they don’t rot and release odor. 


If your fish tank smells like it should not, you need to get to the root of the issue. 

It could be ammonia, which is dangerous for your fish, or it could be chlorine, which is likewise harmful.

The unmistakable smell of rotten eggs indicates that hydrogen sulfide is being released by anaerobic bacteria.

A clean and healthy tank should not release any strong odors. Improving the cleanliness of your tank will generally eliminate any unpleasant smells.

The next time something smells fishy in your aquarium, you know what to do. 

Thanks for reading.


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Pet Aquariums

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