6 Reasons Your Fish Tank Smells Bad And Is Cloudy

Keeping a fish tank clean is a vital part of owning a fish tank. It will reduce smell, keep the water clear, and keep the fish happy.

But if you are uneducated on how to maintain a fish tank, it will be hard to keep things running smoothly.

You may run into a bad-smelling fish tank or a fish tank with cloudy water when you first start keeping fish because there is a learning curve and a lot of trial and error.

But don’t get down on yourself- with these simple tips, you will be able to keep your fish tank in perfect condition.

Why Does My Fish Tank Smell Bad?

No one wants a fish tank that smells bad; it will discourage new fish owners from pursuing the hobby and make old fish owners want to quit. A bad fish tank can make your entire room, or even house, unenjoyable, which defeats the purpose of a fish tank.

The main thing that makes your fish tank smell bad is bacteria, and that bacteria can come from many different sources. These sources include dead fish, excess food, decomposing plants, a dirty filter, your substrate, or your water conditioner.

Dead Fish

Dead fish are the most common cause of fish tank odor. It might take you several days to notice that a fish is dead if it was hidden somewhere in a corner you can’t reach. The dead fish will be leeching oils and proteins that are bubbling up to the surface and evaporating; remove the fish as soon as you find it.


If you give your fish too much food, the uneaten food will fall to the bottom of the tank and promote bacterial growth. The bacteria will grow exponentially and release gasses that smell bad. 

Decomposing Plants

If you have a lot of plants in your aquarium, it may be hard to notice if one has died and is decomposing. The plant will be black and slimy and create a terrible decomposing smell.

Dirty Filter

Everything that can create bad smells gets sucked into your filter. It is common for the filter to be much dirtier than the tank itself; that means it is doing its job. If you don’t clean out your filter, your water will smell bad.

Your Substrate

If the bad smell from your fish tank smells a lot like rotting eggs, then the culprit is probably your substrate. Sand that has been compacted over time can have areas where no oxygen can reach, and then waste, and bacteria get trapped.

Water Conditioner

Sometimes, the water conditioner smells strange. This is because of the chemicals in it. If you put too much into your tank, it may be causing your tank to smell bad.

Many tropical fish swimming in a dirty aquarium with murky water.

How Do I Get Rid of the Smell In My Fish Tank?

Remove Dead Fish

The first thing you should do if your tank smells bad is to look for dead fish. Check in all the cracks and crevices of your tank (there may be a lot)! Once you find the fish, carefully remove and dispose of it.

Use Less Food

If you see a bunch of food stuck at the bottom of your tank, that is a surefire sign that overfeeding is causing the smell in your tank. First, remove all of the excess food at the bottom of your tank, being careful not to stir it up in the process. Next, be sure to only feed your fish as much food as they can eat in two minutes.

Remove Dead Plants

If you can’t find dead fish or any excess food, your next best bet is to look for dead plants. They won’t be hard to miss. They will break apart while you’re removing them, so it is a delicate process.

Replace Your Filter

Your filter is where all the gunk and goo of your tank ends up. If you don’t clean your filter often enough, all of that goo will start to stink up your tank. Depending on the kind of filtration system you have, you may have to replace the filter itself, or you may have to rinse it out.

Replace Your Substrate

If you see that your substrate has become hardened, it is harboring bacteria, and you need to replace it. First, take all the fish and water out of your tank and transfer them to a holding tank. Next, replace your substrate and clean the tank while it’s empty, and then transfer the fish and water back into the tank.

Measure Your Water Conditioner

Have you just been eyeballing your water conditioner? This is not only bad for your fish, but it can also make your tank smell funky. Be sure to properly measure your water conditioner before adding it to the tank.

Why Is My Fish Tank Cloudy?

Dissolved Constituents

Dissolved constituents are things like heavy metals, silicates, and phosphates. The pH of your water is probably way too high. Dissolved constituents can make even brand new tanks cloudy.

Bacterial Bloom

Bacterial bloom often happens in the first few days or weeks of having a tank. This is because the tank hasn’t had time to develop bacterial colonies that will clear the waste from the water themselves. Eventually, your tank will become self-cleaning.

Too Much Light

Too much light will cause algae to grow. You may have the aquarium in direct sunlight, or you could be leaving the lights on for too long. This will turn the tank green.


Nitrates will develop over time in the aquarium because of fish waste. High levels of nitrates can cause algae and turn the tank green.


Phosphates may be coming from decaying matter like excess fish food or from the water itself. Your tap water may have excess phosphates in it, so you should run a test. Extra phosphates in your water will encourage algae growth, which will turn the tank green.

How Do I Get Rid of a Cloudy Aquarium Water?

Rinse the Gravel

If your tank gets cloudy right away, it’s probably because the gravel wasn’t washed sufficiently. Drain the tank and transfer the fish into a holding tank. Now wash your gravel until the water is running clear, and set your tank up again.

Fix the pH

If your tank is cloudy, it may be because of a high amount of dissolved constituents. This will make the pH of your water high or alkaline. Treat the water with a water conditioner to fix the pH of the tank, or you can also use Reverse Osmosis water.

Wait It Out

Bacterial blossoms happen when there are bacterial blooms due to things like excess food or decaying plants. During the break-in period of your aquarium, it will not yet have the bacterial colonies required to self-clean. Soon, there will be good bacteria developed in your tank that will clean the tank for you.

Keep Your Tank Clean

Remove debris like uneaten food, vacuum the gravel, and perform partial water changes frequently. Only feed your fish as much as they can eat in two minutes to avoid excess food sinking to the bottom of the tank and causing bacteria.

Move Your Tank

If your tank is in direct sunlight, that can be encouraging algae growth. Move your tank out of direct sunlight if you notice that your tank is green. This is the first step you should take if you notice algae in your tank.

Run A Water Test

Test your tap water for phosphates because phosphates can cause algae to grow, which would turn your tank green. If you have high phosphate levels, you will have to use Reverse Osmosis water or a phosphate remover. You can also reduce how much you feed your fish.

How to Prevent a Smelly and Cloudy Fish Tank

Change the Water

Take out 25% of the water from your tank and replace it with conditioned water that is from your cold water tap. Make sure that you’re treating the new water by making it the right pH and adding conditioners.

Clean the Gravel

You should clean the gravel before you put it into the tank and periodically throughout your tank’s lifetime. First, rinse your gravel until the water runs clear. Then, you can buy a gravel vacuum at a pet store to periodically remove any decaying debris or bacteria from between the gravel.

Rinse the Filter

Every month, turn your filter off and remove it from the aquarium. Wear a glove, take the debris out of the filter’s sponge, and then scrub the tubes and casing of the filter under cold tap water with no detergent or soap. A filter that is well-maintained helps keep fish alive because it contains good bacteria.

Avoid Overfeeding

Fish should only have an eating timeframe of two minutes, so anything they don’t eat during two minutes should be scooped out. Eventually, you will know roughly how much food they will eat. If you let food sink to the bottom of the tank, it will develop bacteria and make your tank foggy and smelly.

Get Freshwater Fish In a Big Tank

If you are a beginner, get a big tank and freshwater fish. The bigger tank will stay cleaner because the water won’t be in such a tight space, and the water conditions will stay more stable. Freshwater fish can also handle environmental changes better. 

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Is it bad if my fish tank is cloudy?

Bacterial blooms are very common in new tanks while there is a buildup of beneficial bacteria that will consume ammonia. The water is cloudy because all of the bacteria are free-floating. The cloudiness will settle down in a few days, but if it doesn’t, it’s worth investigating other causes.

How Do I Make My Fish Tank Water Crystal Clear?

Healthy plants will naturally filter the water and consume compounds like iron and ammonia, which can cause algal blooms or bacterial blooms.

You can never overdo it on a filtration system as long as the flow isn’t blowing your plants and fish around too much; having water that isn’t filtered enough will surely be cloudy.

You can also add clarifiers to your water which are chemicals that quickly fix cloudy water, depending on the cause.

Will Cloudy Water Hurt My Fish?

Some freshwater species actually prefer cloudy water if their native habitats are muddy. Freshwater fish are incredibly resilient and can handle a lot. But brown or green water indicates algae bloom that can be harmful to fish.


There is a lot to learn about keeping fish! If you want to avoid smells and keep your water clear, there are action steps you can take, both to be preventative and to fix an existing problem.

Bad Smells

One thing that can make a fish tank smell bad is dead fish. They are the most common cause of odor in fish tanks. Also, overfeeding your fish will cause an excessive amount of food to collect at the bottom of the tank

Remove dead fish and only feed your fish as much as they can eat in two minutes.

Decomposing plants and a dirty filter will both cause bacteria that will make your fish tank smell bad. Be sure to get rid of any dead plants and clean out your filter regularly.

Cloudy Tank

Bacterial blooms can cause a cloudy tank. Bacterial blooms happen when the tank hasn’t yet developed a healthy bacterial ecosystem. This is something you just have to wait out.

Too much light causes algae. Don’t keep your aquarium in direct sunlight. Phosphates and nitrates also cause algae.

Rinsing and vacuuming your gravel will help keep your fish tank clean. Make sure you have the right water pH as well.

To change the water, remove 25% of the water and replace it with cold, treated water.

If you are just starting off, try freshwater fish in a big tank. Big tanks stay cleaner for longer because they are more stable since they have more water. Freshwater fish can also survive many environmental changes.

Final Thoughts

Now that you know all there is to know about why fish tanks smell bad and get cloudy, you can keep a clean, healthy fish tank that is sure to wow your guests!

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