Why Your Fish Tank Smells? & How You Can Fix It

It’s disturbing to suddenly smell weird odors inside your home. It’s even more frustrating if the stench you smell comes from your fish tank. In that case, you won’t only worry about the funky smell, but the health of your aquatic friends as well.

Fish tanks don’t usually smell excessively bad. In the long run, though, the stench may become more noticeable. If you place your nose directly over your aquarium water and notice a disgusting smell, you need to take immediate action.

To help you with this, we’ve summarized below the common reasons why your fish tank smells. We’ve also included preventive measures and damage control you can do in case of a smelly aquarium.

Short Answer

There are many reasons why your fish tank reeks of unpleasant odor. One of the obvious causes of your aquarium fishy smell is a dead fish. Other decomposing organic matter, such as dead plants, fish food, and fish waste, could also contribute to the stinky odor of your fish tank.

Aside from the noticeable odor, you might also observe cloudiness or discoloration in your aquarium water. Murky water could be a sign of contamination of decaying substances in your water.

Other reasons why your fish tank smells are contaminated substrates, dirty filters, and smelly water conditioners.

Whatever reason you have a stinky aquarium, it’s a good idea to maintain your fish tank. Regular cleaning and replacement of your aquarium water could prevent any odor or color from materializing.

Long Answer

Your fish tank isn’t supposed to give off a horrible smell. If it does, you need to inspect your aquarium to find out the cause of the stench.

Below are some of the things to look out for when checking your aquarium and how to fix them.

Dead Fish

Like any other dead organism, dead fish can smell bad. If your fish has been dead for too long and is already rotting, the stench could easily saturate your entire room.

Luckily, it’s easy to solve a smelly aquarium due to a dead fish. Once you discard the dead fish, the smell would instantly go away.

How to fix it:

If you have a mini fishbowl, spotting a dead fish shouldn’t be difficult. You would easily detect it floating on your aquarium water surface.

However, the case is not the same for a big fish tank with plenty of aquarium furniture and various fish species. In this situation, it would be a big help if you keep an inventory of your fish, so you could easily keep track of them.

If you don’t have such, you can check on each plant, rock, and decoration inside your fish tank for any decaying fish body. Be sure to check areas that your fish can hide and fit into.

If you have an open tank and jumping fish, check the areas around your aquarium in case your fish escapes.

After finding your dead fish, immediately take it out of the water using a fishnet. After which, dispose of it by either burying it in your garden or throwing it in your organic waste bin.


Feeding your fish excessively can be harmful to your fish’s health. If you give them more food than they can consume, these food particles will sink to the bottom of your fish tank and rot. The decaying fish food would accumulate over time, thereby harming your fish and causing an awful smell.

How to fix it:

To solve the issue, regularly clean your substrate and filter. Use a gravel cleaner or vacuum to clean food and waste debris from your substrate easily. Clean your filter correctly so as not to remove the beneficial bacteria in it.

The next time you feed your fish, provide only enough amounts of fish food to minimize the rotting leftover food in your fish tank.

Fish Poop

Excretion is part of every organism’s metabolic process. Thus, after your fish eat, you can expect them to eliminate waste. And guess what, the waste of your fish goes nowhere else but in your aquarium water.

If you have plenty of fish in your tank, you’ll be dealing with more fish poop. Consequently, when these organic wastes decompose, your fish tank will stink.

How to fix it:

Like how you fixed a smelly fish tank due to overfeeding, you can also resolve one due to substantial fish poop by cleaning the substrate and filter.

To avoid having to deal with excessive fish poop, do not overstock your aquarium. Only buy fish that are right for the size of your fish tank.

Decomposing Plants

Plants are another organic element in your fish tank. If your entire plant dies or parts of it rot, they will turn brown or black. They will also become slimy. When this happens, your decaying plant will give off an unpleasant odor and affect the quality of your aquarium water.

Not only should you be watchful of your dead aquarium plants, but also algae. Algal growth in your fish tank can smell putrid and look disgusting.

How to fix it:

Scour your aquarium for any dead plant. If an entire plant dies, you should take it out of the water. If only a part of your aquarium plant withers, you can prune your plant to remove the rotting portion safely.

It could be alarming if your plants are dying. Thus, to keep this from happening, you should take care of them as well. Give them their required light and nutrients to save them from dying.


Although your aquarium sand and gravel are not organic, they could smell bad due to the accumulation of fish food and waste.

As your substrate gets agitated by your fish, these organic materials will be embedded with sand. When that happens, anaerobic bacteria will feed on the leftover food and poop and release rotten-egg-smelling gases in the process.

How to fix it:

If you have smelly substrates, you need to clean them using an aquarium substrate cleaner or vacuum. Ideally, you should stir your substrate to dislodge buried bits of organic matter. It’s also a good idea to regularly agitate your gravel to prevent the buildup of stinky gases. Make sure to clean the substrates under your plants and aquarium ornaments.

Dirty Filter

Likewise, your tank’s filtration system is non-biodegradable, but everything that’s trapped in it is. Your aquarium filter has both a biological filter media and a chemical filter. The former contains anaerobic bacteria which treat nitrites and ammonia in your aquarium water. The chemical filter component, on the other hand, removes harmful chemicals and substances from the water.

Because of this efficient mechanical filtration system, organic matter can get trapped in your filter media. When these trapped particles rot, your fish tank will smell bad.

How to fix it:

Clean your aquarium filter properly to avoid any damage and prevent killing the beneficial bacteria in your filter media. To do this, simply remove the filter and wash it in the water that you’ve removed from your tank. Take out the gunk and dirt in the filter as you wash the filter.

Clean your aquarium filter at least once a month when you do a partial water change to prevent your fish tank from smelling musty.

Water Conditioner

Water conditioners are vital for your fish’s survival. They are used to treat tap water to remove chlorine or chloramine before putting the water in the tank. However, because water conditioners contain sulfur, they could also be the source of the stench in your fish tank.

How to fix it:

It’s normal for pure aquarium conditioners to smell like rotten eggs due to their sulfur content. But, the smell should dissipate once you mix the conditioner with water.

If the smell does not go away after a few minutes, you may need to change your water conditioner and choose a product that doesn’t have a strong sulfur odor.

Conclusion – Why Your Fish Tank Smells?

Having a smelly fish tank in your home can be embarrassing and bothersome. The smell is not comforting and relaxing, and you may not be able to focus on your chores. Moreover, it would be humiliating if you have guests at your house, and the smell of your aquarium stands out.

Aquarium water contamination, dirty water substrate, dirty filter, and smelly water conditioner are common causes of a smelly fish tank. Fortunately, the solutions to these problems are quick and straightforward.

If you have dead fish, excess fish food, decaying plants, and fish waste in your aquarium water, you need to eliminate these substances and replace your aquarium water. Use a gravel cleaner to clean leftover fish food, fish poop, and smelly substrates.

If your aquarium filter is to blame for the horrid smell of your fish tank, you can either clean it or simply replace it with new ones.

Lastly, if your water conditioner causes the unpleasant smell of your fish tank, it may be time to switch to another product, preferably one that’s sulfur-free.

In any case, smelly fish tanks call for cleaning and maintenance. To do this, you will need to empty your tank to clean everything inside it. Start cleaning the aquarium walls and then the substrate, plants, and other aquarium ornaments you have. Then, clean your aquarium filter and replenish the water.

When doing maintenance, partial water change would suffice. Doing these things regularly could help prevent any odor in your fish tank from developing.

If you diligently clean your aquarium, your fish friends will thank you for keeping their home clean and healthy. On top of that, your family will also commend you for getting rid of the stinky and fishy aquarium smell.


Leave a Comment