Smelly fish tank – 7 Ways how to fix it

Smelly fish tank – A fish tank that is in optimal condition does not smell. However, it can happen that your fish tank water can give off a bad smell and then you have to take action.

Smelly fish tank water is the result of bacteria that break down organic substances, releasing gases. This can be the result of a dead fish, overfeeding, dead plants or rot in the bottom. The cause can also be a clogged filter or poor maintenance of the aquarium.

Below I have further explained these problem points and you can read how you can tackle the smelly smell. Finally, some tips for regular maintenance of your aquarium to prevent these problems.

7 Causes of smelly fish tank water

1. Fish tank water smells like fish

Unfortunately, a fish does not live forever, and one day it will give up the ghost. When a fish dies, it usually floats to the top of your tank on its own, but that’s not always the case. Some fish like to hide in plants or decorations, and if they give up the ghost, you may not notice it right away. Especially in large fish tanks where quite a few fish are swimming around, you will not quickly notice that one is missing.

Over time, the fish will decompose, giving off a foul-smelling odor. You will quickly recognize that smell as rotten fish. As soon as you smell it you immediately recognize the smell. You really don’t have to be a specialist for that.

dead fish smelly fish tank

A dead fish in your aquarium causes stench and the solution is (dead) simple: remove the fish from the water.

The foul odor will soon disappear after you remove the fish from the tank. It is wise to check your water values! With this you can immediately see whether there are toxic substances in the water, and you prevent more fish from dying.

2. Too much food for the fish

If you give the fish in your tank too much food, or food left over after feeding, it can settle on the bottom of the tank. The fish food can then settle between the gravel and the pebbles, causing it to rot over time.

The fish food can also be sucked up through the filter, so that it no longer comes out of the filter. Here, too, the food will decay and begin to give off an unpleasant odor.

Feeding fish too much every now and then can do no harm in many cases, but make sure you don’t systematically give too much food. Better a little too little than too much.

The next time you feed the fish, pay close attention to how much they can eat within 1 to 2 minutes (varies by fish species). If anything remains, it means that you have simply given too much food. Do not let this excess food float around in the aquarium, but scoop it out with a net. There is a good chance that the fish will no longer eat it and will sink to the bottom.

If you think that overfeeding is the problem with the smelly aquarium water, then it is wise to clean your bottom and to clean part of your filter. This will give you a fresh start and the water will smell neutral again at some point.

3. A fish tank plant has died

Plants in your fish tank are continuously growing and it is possible that an old piece of plant dies. It is also possible that your fish like the plants so much that they come loose from the bottom and float around in the fish tank.

A dead plant will usually settle on the bottom of your aquarium after which it is broken down by the bacteria, or the plant parts are simply sucked into your filter. During the rotting, gases are released, causing the aquarium to smell.

If you notice that a plant (part) has died, remove it immediately from the water. This prevents it from rotting and giving off a foul odor. Also make sure that you have a good mix of different plants in your aquarium and that it is not overcrowded.

4. Too many fish in the aquarium

A lot of fish means a lot of waste products, such as poo, in the water. Overfeeding can also cause your fish to produce a lot more waste and your filter can struggle to filter it out in time.

Some fish simply produce more poop than others, so it’s important to know the size of your tank to keep this in balance. Goldfish, for example, are known to be major polluters and therefore also need a large aquarium. Here you can read how big a goldfish aquarium should be .

If you think that overpopulation is the cause of smelly water in your tank, you should simply reduce the amount of fish in it. For example, consider a second aquarium or give the fish away to a friend or trader. A healthy living environment in the water is more pleasant for the fish. You want the best for them, right?

After a few days the aquarium water will smell neutral again if this was the problem. Do you prefer faster results? Then do a part of the water change, so your filter doesn’t have to work as hard.

5. Something has rotted in the soil

If your tank smells like rotten eggs (sulfur), something in your bottom is probably rotting. This can be, for example, plant material or food that has become stuck between the stones.

As soon as this waste slips between the stones, so that no natural flow can take place, it will be broken down by the bacteria. This releases gases that can accumulate as an air bubble in the bottom of your aquarium.

These air bubbles are released when the bottom is touched, for example, during cleaning or by a fish, resulting in a foul smelling air around your aquarium.

Prevent your soil from slipping and the sulfur gases can build up in the soil. You can do this by gently moving the gravel or sand on the bottom, for example, every time you change the water in your aquarium. Pay particular attention to the corners of your aquarium and around plants and decoration.

Read Also: Aquarium Soil – Which One Is Better To Choose

6. The filter is dirty or clogged

Your filter contains bacteria that help break down the ammonia and nitrite in the water. Your filter processes at least 4 times the amount of water in your aquarium and ensures a healthy living environment for your fish.

At a certain point, all those small particles that are retained by the filter become so much that a good flow can no longer take place. As a result, the bacteria work less effectively and simply cannot process the water quickly enough. This will result in water that starts to smell bad.

You should also include cleaning your filter in your monthly maintenance routine. This prevents it from slipping and the aquarium water starts to smell.

7. The fish tank water has not been changed regularly

The above 6 points can all cause odors in your aquarium water. It is therefore important to check these points first and then replace part of your water. This ensures that the bacteria that cause a foul odor do not get the upper hand.

Prevent smelly fish tank

Read Also: Cloudy Aquarium – Why And How To Solve It

Prevent smelly fish tank water with good maintenance

There are many causes for smelly fish tank water and it should be obvious that good maintenance of your fish tank is a good start. Change your water regularly, clean the filters and provide a good living environment for your fish. These are actions that take almost no time and you should therefore include them in your maintenance routine.

Frequently Asked Questions

How long does it take for a fish tank to clear?
In general, cloudy water clears within 5 days of addressing the cause of the problem. Green water due to algae growth can be clear within 5 days, while water with a white haze can be cleared within 1 to 4 days.

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