Aqua Leaves Pattern Google+ Photo (2)

Why Does my Fish Tank Smell?

Fish tanks have smells. It is an irrefutable fact. However, smells need not be bad. In fact, under ideal conditions, aquariums can have soft, pleasant, characteristic smells, depending on the type of water that fills them. Generally, freshwater tanks have an earthy mist, while saltwater tanks can remind you of beaches and oceans. If one’s fish container does not have such aromas associated with it and instead smells a little fishy, it is okay. However, this in no way warrants extreme foul smells that inform you of the existence of a fish tank upon entering its vicinity. If you can smell your tank from a distance, it means something is wrong inside there and must be attended to immediately, as the environment in for the fish would be unhealthy and stressful.

Figuring out why your tank smells bad needs patience and attention. There are several causes of foul odor, and any one of them could be responsible for your fish tank situation.

Dirty Filter

The job of an Aquarium Filter is to, well, filter water. It removes all those things that are not supposed to exist in the water, from dead plants to dead fish to excessive food. However, sometimes, the filter might clog and become dysfunctional. This problem may be caused if the size of your filter is not appropriate according to your tank and fish population size. Therefore, while it might be functioning fine by its potential, it might not be enough for your tank’s needs and allow the building up of nitrates and phosphates in the water. These nutrients nourish bacteria, which in turn produce hydrogen sulfide gas, a gas that smells like rotten eggs.

How to Fix it?

  1. You can determine whether the problem lies in your filter by removing its cartridge and analyzing it if it smells horrendous and looks visibly clogged, it might be a good idea to rinse it thoroughly and then reinstall it.
  2. If the above doesn’t work, then you might have to replace the filter. In fact, before fixing a new cartridge filter, you should remove the entire filtration system and clean it thoroughly.

Dead Fish

Most of us don’t like to hear it or acknowledge this fact, but fish do die. No matter how much we love them, we cannot make them immortal. Another point is that dead things rot, and rotting causes emanation of bad smells. Therefore, it is reasonable to consider that the foul stench coming from your aquarium might be because of a dead fish.

While dead fish do tend to float to the surface, this might not always occur in a tank. Sometimes, the fish might get stuck in the filter, or under the rocks in the bottom or within the plants and decorations, and you may not realize until days after the demise of the poor being. Therefore, if a fish seems to be missing from the population, you might want to check for its dead body in the tank.

How to Fix it?

  1. Roll calling your fish every morning is a good idea. While it does require an immense amount of patience to check if all the inhabitants of the tank are good and alive, its importance outweighs the struggle. Make sure that no fish are missing. If there is one, locate and remove its dead body.
  2. If your Aquarium does not have a lid and you have fish that like to jump out of the water, you might also want to check the area behind the tank, for some fish might have jumped out but never made it back.
  • There isn’t much we can do to make sure that the fish live forever. However, we can make their lives longer and healthier by ensuring a proper diet and a clean water environment.


Owners, often in their love, tend to overfeed their fish. But it is vital to realize that fish can only eat as much. Once their appetite is satiated, they will not eat more unless they are greedy. This means that either of the following two consequences is likely: i. the fish do not eat the excess food, and it settles down on the bottom of the tank and begins to decompose there; or, ii. The fish do eat the food, develop digestion problems, and produce more waste than usual, which pollutes the water. There might be another issue with the food you are feeding- the food might not be suitable. All feeds are not all fish. Each specie has a particular dietary requirement that must be kept under consideration when feeding. If you supply the wrong food, the fish might develop indigestion problems and egest an unprecedented amount of waste, which makes the water smell foul.

How to Fix it?

  1. Check the bottom of your tank for the remains of excessive food. If you find them, remove them.
  2. It is advisable also to check the filter. Bits of food tend to accumulate in there. If you find the screen clogged, clean it thoroughly, and then reinstall it.
  • For future reference, make sure you feed your fish just enough. This thing requires keen observation of your fish and trial and error. As a rule of thumb, only put enough food your fish can finish in about 5 minutes. If still unsure, consult your local pet store/ vet for further guidance.

Dead Plants

Plants are essential for aquatic life. They not only enrich the water with crucial nutrients for fish but also produce oxygen and add an aesthetic element to the tank. However, plants are as living beings as fish. They are involved in an everlasting process of growth and regeneration. If these conditions are not apt, they might also die. Having dead plants in your aquarium means living matter decomposing, which means terrible smell.

How to Fix it?

  1. One of the good things about dead plants is that they are easy to spot. Before dying and falling to the bottom of the tank, plants tend to turn a slimy brown/ black color, which often stands out. If you find plants in such a state, it means that it is time to remove them.
  2. You should also check the filter, for the dead remains of the plants might have accumulated there and clogged the cartridge. Cleaning the screen should help do the job if the problem lies within there.
  • There are specific precautionary measures that you could undertake, as well. One of them would be not to overpopulate your tank with plants. Just keep and maintain an adequate amount of them. Second, you could get underwater species that live on dead matter. They naturally keep the aquarium clean and healthy and take off the burden from your shoulders.

Fish Poop

Poop stinks, and that is an undeniable, irrefutable fact. If there is an adequate amount of fish waste in the tank, it is easily regulated by the filter. However, often people tend to overlook the basic equations: too many fish = too much poop and over-feeding = too much poop. In case your fish are egesting a lot of waste material, the tank filter might not be able to deal with the situation and get clogged as a result. This accumulation would allow excrement to build up, which would eventually decompose and give rise to a putrid stench.

How to Fix it?

  1. Check your tank for excrement that might have settled on the floor. If there is a visible build-up, you should remove it.
  2. Inspect your filter for possible clogging. In case it is jammed, have it thoroughly cleaned before reinstallation.
  • For future reference, try to reduce the number of fish in your tank, if the tank and filter capacity is small. You might want to sell off some of the fish that you own. If that is not possible, try getting a bigger tank and a stronger filter.

After you have realized that something about the smell of the tank seems amiss, you need to make sure to investigate the problem thoroughly and explore all possible causes of the matter. If you are not an avid cleaner of the tank, you need to make sure you become one. It is often suggested that once tank water begins to give off whiffs of a stink, one should go for full-blown cleaning. This involves wiping the inside walls of the tank, scrubbing accessories in the aquarium, removing all wilting/ dying plants, removing and cleaning the filtration system, partial or complete water change, etc. One thing to keep in mind is that if you have not indulged in proper maintenance of the tank in quite some time, the chances are that your fish-container would start to smell worse. But that is because you would have uprooted the gunk and waste buried under layers of plants and decorations. After a while, things would settle, and the smell would go away.

Once the deeds are done, make sure never to let the situation become this ugly again. This is achieved by keeping a reasonable amount of fish based on tank size, feeding them an appropriate amount of food, doing daily roll calls to see if one might have died, and timely removing dead plants before they start to rot.

One Response

  1. Angila Debell May 14, 2020

Leave a Reply