Owning an underwater ecosystem should be a fun and exciting adventure that grants you an opportunity to observe another world. If your fish tank smells bad, this is a sure sign that something has gone awry and is in need of your immediate attention. There are many different reasons behind the odorous scent that your aquarium can put off. To help you diagnose the troubles, here is a handy round-up of the most common reasons why a tank can smell strange and what to do about it.
Rot
A decaying critter (fish, snail, other invertebrate) that has been trapped behind part of your tank décor, a plant, or even stuck in your filter system, a dying plant or sickly creature can put off a terrible odor. The first thing to do is check to make sure that your fishy family is happy and healthy. Next examine any nooks and crannies to ensure that all fish are accounted for. Another source of unpleasant odor stems from any plant life that has not been properly taken care of. Parts of plants can rot underwater contributing to a nasty and lingering smell. Lastly, uneaten food from overfeeding that goes uneaten by your tank’s population is often left to rot in the water and can be a third source of unpleasant odors.
Water Causes
The next category of reasons why your fish tank smells is due to issues with your water quality. Insufficient filter maintenance or adding unnecessary chemicals are two main reasons why you could have an odor. Be sure to perform routine tank maintenance that includes checking your filter system and cartridges, cleaning as necessary and adjusting your chemical additives to prevent unnecessary or undesired odors by changing approximately 10-15% of your tank’s water weekly. Be sure to avoid water conditioners that are high in sulfur (smell like rotten eggs).
Improper Cleaning
Just like your house, keeping a clean environment is part of maintaining a thriving environment. When it comes to your aquarium, a stink-free tank can be counted on when you perform regular maintenance care and conduct the proper cleaning tasks. Don’t forget to wipe down the small places that can accumulate waste and bacteria for a clean, smell-free fish world!
Feeding A Pellet Or Flake That Is Too Large For Your Fish To Properly Eat
Remember you want your aquatic friends to digest as much of the food you feed as possible. This means picking the proper sized pellet or flake is as important as choosing the proper nutritional offering. Pellets or flakes that are too large tend to be blown out the gills during meal time and this residual food can cause odor issues as it decays. Smaller pellets and flakes are easier, for even the largest fish to digest and take in and also easier for your fish to enjoy. Remember, smaller more frequent feedings are also better for the health of your fish population.
If you still can’t locate the source of a nasty smell, contact your local fish professional and have them help identify the issues in your aquarium so you can get back to enjoying this amazing hobby and reveling in the beauty of your fish!
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If your fish tank smells like sulfur, or rotten eggs, it usually means you have a serious water bacteria buildup, a chemical imbalance, or a problem with your aquarium pump or filter. This type of environment is stressful and unhealthy for your fish; it needs to be taken care of as soon as possible. Letting the problem go for too long can make the condition worse; it can kill your fish.
Fill up a bucket with equal parts aquarium water and same-temperature dechlorinated tap water, and transfer your fish from the tank into the bucket using a net. If it's going to take you a while to clean your tank, put the bubbler hose from your tank into the bucket to make sure the water is oxygenated. Remove plants and decorations after you move the fish, putting them in a separate bucket for cleaning.
Use a siphon to drain all of the water from your fish tank and dispose of it by flushing it down the toilet. If you don't have a siphon, you can use a plastic cup or a small handheld water pitcher to remove the water. If you can safely move your tank outside to clean it with a garden hose, that's your best bet. If it's too big, use a water pitcher to flood the bottom of the tank and the gravel with fresh water and stir the rocks with a gloved hand or a long-handled wooden spoon. Continue siphoning and stirring the water, as you're going to be getting a lot of debris out of the tank.
Use a softer scrub brush to clean the inside of your tank walls, and use a razor blade to remove algae buildup. Continue flushing the tank with clean water until it runs clear. Move on to clean the plants, decorations and filter in the same manner, using a scrub brush and clear water. Refill the tank to its normal level using dechlorinated tap water. Allow the water to reach the appropriate temperature for your particular breed of fish, then add your plants and decorations into the tank before returning the fish.
Get into the habit of removing uneaten food so it doesn't clog up your filter or cause your tank to become so dirty that you get another imbalance that results in an unhealthy water environment and a sulfurous smell. Do a partial water change every week or two by taking out 10 percent to 20 percent of the water and replacing it with dechlorinated tap water. If you see algae building up inside your tank, use a long-handle scrub brush to remove it, or get an algae-eating fish like a plecostomus to help keep the tank clean. Talk to your vet about other commercially produced water additives that can safely help you cut down on smells in the future.
Does your fish tank smell bad? If so you have a problem. An aquarium should never smell foul as that’s a sign of rot and decay.
Your fish are in an unhealthy environment and if they die they will further pollute the water, compounding the issue.
Let’s look into some causes and fixes for smelly aquarium water!
Why Does My Fish Tank Smell Bad?
Here are a few common reasons why you fish tank may smell bad:
Check for Dead or Decaying Inhabitants
One of the most common reasons fish tanks smell bad is because one or more of the inhabitants have died. If you don’t get to them within a few hours intestinal and environmental bacteria and fungi begin breaking down the fish.
They release ammonia and sulfurous compounds that make an unmistakable odor. Since dead fish tend to float due to their swim bladders and decomposition gases they should be easy to find and remove.
A few hours after removing the rotting fish, sniff your tank water for foul odors and check the water quality using aquarium test kits (see below). Water changes are almost always a good idea if a fish dies in mysterious circumstances but these tests will help narrow down the causes.
Perform Tests on the Water Chemistry
Testing the parameters of your aquarium water will go a long way towards solving the mystery of a stinky fish tank!
A sure sign that leftover food or a missing fish is rotting is a spike in Ammonia or Nitrite. In a healthy aquarium your Nitrifying bacteria are hard at work breaking down Ammonia into the less toxic Nitrite and Nitrate.
This is the basis of the aquarium Nitrogen Cycle. However they can be briefly overwhelmed if there’s suddenly too much of either substance to feed on. Also, if your Nitrifying bacteria have been killed off for some reason you may see a spike in Ammonia that can even lead to fish deaths.
Most aquarists only keep pH and Ammonia tests kits. However I recommend keeping an Aquarium Master Test Kit on hand. You may not always need to test for Nitrate and other parameters. But eventually you will and buying each kit individually costs significantly more over the long run.
Also, if you don’t have a test kit readily on hand most pet stores will perform the tests if you bring in a fresh water sample. Make sure it’s no more than a couple of hours old for an accurate reading. Bacterial action, sunlight, and temperature can all affect water chemistry over time.
Are You Overfeeding?
Overfeeding may be the most common reason your fish tank smells bad. Aquarium fish will gorge themselves because they have wild instincts. In nature they can’t count on food being continually available so they will stuff themselves at every opportunity.
Watch your fish when feeding. When full you’ll often see them instinctually snapping up flakes only to chew them and spit them right back up because there’s no more room for food.
As a rough rule of thumb for small community fish like Bettas and Tetras you can estimate their stomach to be as large as their eye. Only provide as much food to fill that space per feeding but feed 2-3 times per day.
If too much food goes uneaten it begins to rot, fouling water chemistry and creating a distinctive aroma.
How Do I Fix Smelly Aquarium Water?
Here are a few of the most effective ways to fish a foul smelling fish tank:
Look For Signs of Stress
Stress isn’t a cause of smelly aquarium water but rather a symptom of it. Investigate to see how your fish and plants are behaving; it may give you clues to how to proceed.
Signs of stress in fish include:
- Clamped fins
- Rapid breathing while inactive
- Staying near the surface
- Pale coloration
- Frayed or bloodshot fins
Signs of Stress in Plants Include:
- Pale or dead leaves
- Rotting stems or roots
- Holes forming in leaves
Any of these can indicate conditions like disease, elevated Ammonia, Nitrite, or Nitrate, or something else that’s related to the foul water aroma.
Massive Water Changes
Water changes are one of the main tools in the aquarist’s arsenal. While often time-consuming and inconvenient there’s no better fix for a smelly tank than filling it with fresh, treated water.
However large water changes should always be done infrequently because changing more than 40% at a time can be stressful itself. If you don’t perfectly match parameters (pH, temperature, salinity, hardness) you’re causing a significant shift in chemistry to happen all at once.
Tank bred aquarium fish are quite flexible when it comes to chemistry. But if they are already weakened by elevated ammonia or a disease a sudden pH swing can wipe out your tank.
Since there’s a good chance your fish are stressed due to a toxic agent in the water I recommend using tap water conditioners like Seachem Prime that contain slime coat stimulants. A healthy slime coat bolsters the disease and chemical resistance of all fish.
Check and Clean Your Filter
Is your filter media clogged with slowly decaying food or a swept up fish carcass? The media may need rinsing or replacement. Healthy filters tend to grow thick colonies of bacteria to break down organic and nitrogenous wastes.
However these bacteria sometimes become so numerous they prevent the free flow of water. That doesn’t mean you should throw out the entire colony, though! That’s one of the main causes for New Tank Syndrome in established aquariums.
A simple rinse and squeeze will help media thick with bacteria flow freely again without risking elevated ammonia, nitrites, or nitrates.
If you don’t have a filter for your fish then it’s about time you considered getting one. Betta and Goldfish keepers that go without filters are going to run into the problem of smelly water constantly because there’s no room for beneficial bacteria to grow.
Even a simple sponge filter will go a long way towards providing extra surface area for bacterial colonies and mechanical filtration for suspended particles.
Chemical Fixes for Smelly Water
In my opinion chemical fixes should always be the last solution for smelly aquarium water. They rarely address the problem at its source and you risk letting the unknown issue fester by simply eliminating the odor.
However these agents are extremely effective and work well in tandem with the above solutions. Seachem in particular makes great products for fine tuning your aquarium’s water chemistry. If your fish tank smells bad Seachem Purigen is a rechargeable resin that chemically binds suspended organic compounds.
Conclusion
There are several reasons why your fish tank might smell bad. Decaying fish or food and stagnant water are the most common reasons. Fortunately they can be quickly and easily treated with a little investigation into their causes!