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Saltwater Fish

Why Does My Fish Tank Smell

By April 21, 2020April 25th, 2020No Comments
why does my fish tank smell

If you have a well maintained aquarium, you may never have had this issue before, but sometimes your fish tank can smell bad. This goes for saltwater, freshwater, and reef tanks.

When we are talking about a bad odor from your tank, we don’t mean you can catch an odor when you put your nose right next to the surface of the water. Most if not all fish tanks will have some odor to it. This is about any foul odor that you notice while observing our display tank from a normal range.

The main reasons that your fish tank smells is due to improper maintenance which causes excess nutrients.

There are multiple issues that can cause this, and we will take a look at the causes and remedies so that you can enjoy your display tank without holding your nose.

What Causes My Aquarium To Stink

dead fish in aquarium stinks

A Dead Fish or Other Creature

This may or may not be easy to identify, depending on the type and size of your tank. If you have a small handful of fish, and you see that one is missing, you have somewhere to start. However, if you have a very large tank with a lot of fish, it may be more difficult to notice a missing fish or hermit crab.

A dead creature will slowly decay which will cause a spike in your ammonia levels. If you have ever smelled a rotting fish on the beach, you know what we are talking about. Sometimes just a casual stroll through the fish section at the local grocery store will make people turn around and walk away due to the odors.

Fish Poop

Yes, fish poop. In a normal and well care for tank, this is not an issue. We all know fish poo is in your tank, but if your system does not do a good enough job of removing it, it can build up which causes an excess of nitrates.

Good filtration and beneficial bacteria will normally process this, but the mechanical filter and the bacteria do have limitations.

Too Much Food

Fish seem like they are always hungry, and one of the joys or owning a saltwater tank or reef tank is feeding your fish and interacting with them. The downside is if you overfeed them, the excess will fall to the bottom of the tank and start to decompose which increases your nitrates. This will dirty up your water and if it gets too bad, it may cause some foul odors.

How To Make Your Fish Tank Smell Better

better smelling
  1. Remove any dead fish or animals
  2. Do a large water change, around 40%-50%
  3. Do routine water changes if you were not already doing them
  4. Add Activated Carbon Filter if you are not using one
  5. Consider Adding Purigen
  6. Clean your tank including the inside of your glass
  7. Make sure your mechanical filtration is adequate. If not, add a bigger filter
  8. Make sure you do not have too many fish

To remove the stinky smell from your aquarium, you need to identify the likely culprit. One of the easiest is a dead fish, dead crab, etc. Just dispose of the dead fish, and check your levels of ammonia, nitrite, and nitrate. If any of them are off, you need to take corrective action to bring the levels back to normal. You may have a large tank with a lot of fish, and you may need to check around for one stuck under some rock.

If you have no dead fish, use the standard rule of 1 inch of fish per gallon of your tank. If you are well over that, you will need to re-home some fish to get down to that level. Excess fish can cause too much doo in your tank, which will in turn increase your nitrate levels.

High levels of nitrate can turn your water a yellowish color and it can smell, and in addition to that, it is also very unhealthy for your fish. Imagine being stuck in a city that was overloaded with smog and pollution.

One of the best ways to reduce a stinky aquarium is to use activated carbon. Most people use carbon filters in their HOB, but if you don’t carbon will take pollutants out and it will make your water a little more clear.

Another great option to clear up your water is to use Purigen, and as a bonus it will help make your water crystal clear. You can get a filter bag which is used for tanks up to 100 gallons, place it where there is good flow like your hang on back filter or in your sump.

Purigen is inexpensive and it does wonders for a tank that does not have the best mechanical filtration. It is a bag of tiny synthetic polymer balls that removes nitrogenous compounds from you fish, coral, etc. For around the cup of a latte, this is a no-brainer for a tank that is bordering on too many fish or the hang on back filter is not quite enough.

This is great to add to a nano reef tank that does not use a quality protein skimmer.

Another thing you can do to improve the smells coming from your tank is to improve your mechanical filtration. If you have slowly added more and more to your tank, you are increasing the load of nutrients that it can handle. It may be time for an upgrade on your mechanical filtration.

Do regular water changes. If you are in a spot with an aquarium that smells really bad, go ahead and do a 40-50 percent water change. The best way to remove bad nutrients is through a water change. If you do not do regular water changes, now is the time to start, or your smells may come back.

If you have a saltwater tank, make sure you have a cleanup crew that can manage the waste on your sand bed. Obviously, we are talking about crabs, snails, starfish, etc.

Clean your aquarium. This includes normal maintenance like replacing filter pads, cleaning filter socks, clean the algae off the inside of your glass. Get a magnetic glass cleaner to remove the brown algae off the inside of your glass.


Unless you have a a dead creature, there may be a lot of things that you will need to do to get rid of that fish tank smell. Sometimes it can be fish, it can smell earthy, or it can have a bad sulfur smell to it.

Most of the problems revolve around a lack of proper equipment and bad maintenance habits.


My name is James, and I am the founder of Saltwatercoraltank. I love everything about the ocean, and my main hobby is saltwater aquariums. Currently, I have 3 tanks that I maintain. I have a 130 gallon mixed as my main, and I prefer softies.

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