Aquariums at Home earns an affiliate commission when you buy through links on this site. See footer.

My Fish Tank Stinks! What are the Causes and the Fixes?

It is amazing how easy it is to end up with a stinky fish tank. It is also amazing how easy it is to keep your aquarium from smelling bad in the first place! It is a lot of work maintaining a fish tank and it is a lot of work keeping an eye on the fish’s health as well as the water parameters. Doing these things are not the only reasons that fish tanks start to smell but are the common culprits in most cases.

So, how do you fix a stinky fish tank? Identifying what the cause of the smell is would be the ideal way to fix the smell. Once identified, taking the appropriate actions to remedy the problem would be the next step. 

Fish tanks can stink for a multitude of reasons. Poor maintenance tops the list. This includes but not limited to regular cleanings, performing water changes with the right type of water. Keeping the aquarium out of direct sunlight to help prevent an algae bloom. The list goes on and on.

Honestly, if your fish tank is stinking, it might not be your fault, or it just might not be something you knew about. Either way, I can help you identify why your tank is stinky. You should know, though, that a fish tank will give off some odor. You have living creatures in water sitting in a container in your home, there is bound to be some sort of smell. It just should not be overly stinky.

Lets, get this figured out for you…


Why does my fish tank smell so bad?


To identify why your tank is smelling so bad, you need to know where to check. Here are my suggestions.


  • Your water source could easily be the culprit. If you are using well water or your municipal water supply is not up to snuff, it can cause your tank to smell. I recommend using a reverse osmosis water and if you cannot use RO water, then make sure to treat your tap water.


Tap water conditioners are readily available at your local fish stores and online thru Amazon or other companies. A tap water conditioner will help to clear your water of chloramines and other chemicals. API sells a nice product which can be found on Amazon HERE.


  • I know filtration can be overlooked. It is easy when you cannot see inside the filter to really know what is going on. If you have a canister filter, it is even harder to take a quick glance and see what is going on. Hang-on back style filters are a bit easier to see, if there is any sort of buildup.


The fact is you could have something festering and getting out of control in your filter. Make sure to keep performing regular maintenance on your filters, even when things seem to be running well in your tank. You could have a smaller dead fish in the filter or an algae buildup. If you have a sponge or floss component in the filter, it could be harboring fish poop and all kinds of things. Clean it out at least once a month if not more often.


  • This goes partially with keeping your filter clean. A dirty tank can easily cause it to stink. There are just a few things you must do to keep your tank clean, yet one or two of these things are either overlooked or put on the back burner, occasionally by some hobbyists.
    • Water changes are important, not only to the health of the tank but can improve the smell as well. Water changes help to improve the water parameters mainly to get rid of nitrates.


    • Cleaning out the tank’s substrate could freshen up the smell of your fish tank. I vacuum my gravel to suck up excess food that the fish missed as well as fish poop, dead plant material and maybe parts of a dead fish that got missed somehow.


So, you can see how cleaning your substrate can help to rid of any smells. This task coincides with my water changes. I recommend a water change every two weeks minimum but, if you have a stinky tank, then perform one every week until the smell is much better.


    • Cleaning decorations such as fake plants, rocks and other items should be done at least once a month. It is amazing how much guck and goop can build up on these things.


  • Dead fish can be a problem if you have not noticed one or more have died. I know when you have a large community tank with many different fish, sometimes it is hard to keep track of numbers. In the last 6 months, I have lost a few dwarf cory’s and have no idea how they vanished. Keep an eye out at the back of the tank and at the end of the tube that sucks the water out to the filter as they tend to get stuck there.


  • Lastly, one thing that can cause a real stink in your fish tank is an algae outbreak. There is algae that builds up on the surfaces of everything in the aquarium and then there are algae blooms that happen in the water turning it green, yellow or other colors. Performing regular cleaning or maintenance, as suggested in my previous points, will help to keep algae at bay.


    • A couple other things you can do is to keep your fish tank away from direct sunlight, minimize how long the lights are on and invest in a UV aquarium sterilizer. If you have no experience with one of these, you will be amazed at how well and fast they work to clear up algae.


    • To get your feet wet with one, I recommend THIS ONE over on Amazon. I think you will be amazed at how easy they are to run and how well they work.



Is it Normal for Fish Tanks to Smell?

In general, the short answer is yes fish tanks will smell however, they should not stink.

Fish tanks contain living creatures that poop. The water contains living bacteria that is needed for the parameters to be good for fish to live happy and healthy.

At no point should you ever get a ‘whiff’ of your fish tank and think it stinks. If that ever happens, then either your maintenance is not up to par, or you have a water source issue.


What Should My Fish Tank Smell Like?

A fish tank will have a smell there is no getting around that. If you put your nose right up to the top of the tank, you should be able to smell a somewhat earthy odor, especially if you have a live planted tank.

Even my marine tank gives off an earthy smell. A salty one mind you. The earthy smell will be the algae and most likely living beneficial bacteria in the tank and filter giving off that odor.


What if Your Fish Tank Smells Bad and is Cloudy?

If your water is cloudy it could be that your water has not been cycled yet, or you have an algae bloom. Either way if it smells bad and that is a problem.

One tool I really like for an aquarium is a UV sterilizer. If you have any sort of free-floating algae bloom causing the fish tanks water to turn yellow, green, or brown, a UV sterilizer will clear it up so fast you will be pleasantly amazed.

If you have not cycled your tank’s water properly, do yourself a favor and check out my article on the topic when you are done here. What is cycling an aquarium’s water?

You could also try using a biological enhancer. Biological enhancers have beneficial bacteria and speed up the water parameters getting to the levels they need to be at.

I would even recommend using biological enhancers, if you do big water changes just to keep the parameters in check and the existing beneficial bacteria in the tank healthy. By big water change, I am thinking close to 75% of the tank’s water being replaced.

While you are at it, make sure you clean the substrate (gravel) and the filter.


Why Does My Fish Tank Smell After a Water Change?

It is often difficult to diagnose something like this but what I can tell you is this. When I do water changes, I notice I can smell algae a bit more than usual. It is that earthy odor that healthy algae and beneficial bacteria give off. The best thing about this situation is its not a problem.

When you perform a water change by vacuuming the substrate, you are stirring up the tank and odors will come to the surface. Do not worry about it to much. If you just cannot stand the smell, then you need to clean your tank at least once a week to minimize the number of odors coming from it.



The most important piece to take away from this article is that regular maintenance on your fish tank should help you with most of the reasons your fish tank might start to smell.

Take my suggestion on installing a UV sterilizer and do not be scared to use products like water conditioners and biological enhancers. Those products are manufactured for a reason.

Lastly, consider your water source, especially if you are using well water. Reverse osmosis water is great however, it does lack some minerals. I use RO water for my water changes because it keeps my tanks their cleanest. I then use tap water, because of its minerals, about every 4th or 5th water change.

Good luck and happy fishkeeping!


Related Aquariums at Home Articles

Bare Bottom Fish Tanks. Pros and Cons.

What is a UV Sterilizer?

What is a Dutch Aquarium?

Why Does My Fish Tank Keep Turning Green?

Shrimp Like Creatures in My Fish Tank (How to Get Rid of Scuds)

Scroll to Top