Fish Tank Smells Like Rotten Eggs And Sewage: Reasons, Fixes

No lover of domestic fish is immune from the appearance of a bad smell in the aquarium.

Various factors can contribute to a problem fish tank smells like rotten eggs, and all of them require prompt elimination, because. this is a signal of clearly unfavorable conditions in the habitat of pets.

Why does the water in the fish tank smells like rotten eggs? What to do? You will find answers to questions in the article.

fish tank smells like rotten eggs and sewage

Is it bad if my fish tank smells?

When the balance of an ecosystem is disturbed, the environment changes for the worse. The water becomes cloudy, and a barely perceptible rotten egg smell can turn into an unbearable stench.

Such changes entail adverse consequences for the inhabitants of the aquarium:

  • loss of fish appetite;
  • decrease in the vitality of pets;
  • damage to plants;
  • the emergence and spread of infectious diseases;
  • change in the bacterial composition of water;
  • death of fish and other animals.

Why does fish tank smells like rotten eggs and sewage?

The root cause of the rotten eggs or sewage and the appearance of a bad smell can be the following factors:

  • incorrect operation of additional devices, and accessories for the aquarium (filter, aerator);
  • improper care (overfeeding, rare cleaning, excess soil, unsuitable plants, silting);
  • natural consequences of life (excessive reproduction of fish and microbes, the death of one of the inhabitants of the aquarium).

It is not always possible to determine the source of problems, because. the processes occurring in the aquarium mutually influence each other.

A failure in one area starts a chain of adverse events, and as a result, it is difficult to understand whether the water smells due to poor filter performance, overcrowding or overfeeding.

Main causes of fish tank smells like rotten eggs and sewage:

  • dead fish
  • Poor filtering
  • Overfeeding
  • Improper aeration
  • overpopulation
  • Dust or slit
  • Unsuitable plants
  • Untimely cleaning
  • Excess of soil or substrate

Let’s discuss them one by one in detail

Aquarium rotten eggs and sewage due to dead fish

The fish carcass can go unnoticed for several days, polluting the water and provoking the corresponding smell.

This is typical for spacious aquariums with a large number of animals, plants, and decorations, among which the dead individual often goes unnoticed.

If a dead pet is found, it should be removed immediately and an estimated time of death should be estimated. Further actions of the owner of the aquarium depend on this:

  • renewal of water by a third if the fish died recently;
  • complete replacement of water, if the carcass is loose, soft, traces of decomposition are visible on it.

In the future, it is necessary to observe the remaining fish for several days. It is important to make sure that the other inhabitants of the aquarium are safe.

Fish tank smelling due to Poor filtering

The main function of the filter is delicate cleansing. With its help, aquarium water is freed from various suspensions and quickly enriched with oxygen due to constant movement.

Pollution due to failures of the filtration mechanism manifests itself in the form of an rotten eggs and sewage smell, a film on the surface and suspensions in the water column.

The problem is solved as follows:

  1. Washing the filter.
  2. Elimination of suspensions.
  3. Complete removal of food residues 5-10 minutes after the start of feeding on a permanent basis.

If the above steps do not lead to the desired result, and the water smells bad again, the problem may be a worn sponge inside the filter. It should be replaced.

Some sponges have pores large enough to allow fish feces to pass back into the aquarium. Before buying a filter, you need to consult with a specialist .


Overfeeding is one of the top three causes of bad breath.

Often people overestimate the amount of food fish need and give up more food than they need.

As a result, food remains settle on the ground and decompose, creating favorable conditions for the reproduction of pathogenic microorganisms. Pathogenic microflora not only leads to aesthetic problems in the form of rotten eggs and sewage smell and other unpleasant odors and cloudy water, but also provokes infectious diseases in fish.

To eliminate the smell caused by excessive feed in the water, it is necessary:

  1. Clean the top layer of soil with a siphon.
  2. For one or two days, depriving the fish of food. Short-term fasting will not harm them.
  3. Reduce portions of subsequent feedings by a third.
  4. All food remaining in the water within 5-10 minutes after the start of feeding should be carefully removed.
  5. Evaluate the smell of water after a few days.

Improper aeration

Lack of oxygen, like excess, affects the aquarium environment. The first threatens its inhabitants with oxygen starvation, the second – with excessive saturation of tissues and organs with this gas.

If the level of oxygen supply changes abruptly, the aquarist can expect more serious consequences than a bad smell. The fish run the risk of dying even before changes in the water that can be sensed by the sense of smell occur.

Signs of an emergency change in oxygen levels are as follows:

  1. Fish try to stay near the surface of the water, actively swallowing air.
  2. Those who managed to suffer from hypoxia lie on the ground and breathe heavily, not reacting to stimuli.
  3. Snails are very sensitive to lack of oxygen. In case of danger, they leave the bottom, on which they have been all their lives, and move closer to the surface of the water.

When aeration is set incorrectly but does not reach critical levels, it may seem that the aquarium lives a full life.

However, gradually the signs of an unfavorable environment for fish and plants will begin to increase:

  • fish lose their appetite and become less active;
  • the water becomes cloudy;
  • there is a damp musty smell.

The most reliable way to determine the level of oxygen in an aquarium is to test the water with tests sold at the pet store.

You can help the inhabitants of the aquarium in the following way:

  1. Check filter operation. If not, purchase and install.
  2. Change the water by a quarter if it is dirty.
  3. Set aeration.
  4. An emergency measure is the addition of a solution of hydrogen peroxide to the water. The amount of the drug depends on the volume of the aquarium, an overdose can be fatal for the inhabitants of the aquarium.
  5. In the future, check the oxygen level in the water at least once a month.
  6. Always ensure high-quality filtration and avoid overcrowding.

Fish overcrowiding

Insufficient aquarium size relative to the number of fish increases the risk of rotten eggs and sewage smell. The more inhabitants huddle in cramped conditions, the faster the soil and water become contaminated with food residues and waste products. The latter leads to uncontrolled growth of bacteria, which increases the risk of death of plants and fish.

The problem can be solved only by increasing the living space:

  1. Transfer some of the fish to another container.
  2. Buy a larger aquarium.

The final decision depends on additional factors, which include:

  • the total number and size of living creatures: on average, each fish needs from 1 liter of water per centimeter of the body;
  • the presence in the aquarium of plants and decorations that occupy part of the space;
  • the presence in the house of a suitable place for one large or second small aquarium.

Subsequently, it is necessary to continue to control the number of fish and to resettle them in a timely manner if necessary.

appearance of Dust or silt

Silting of the soil (formation of detritus) cannot be considered a negative factor: it contributes to the biological health of the entire aquarium.

The reverse side of the coin is that an excess of silt leads to disruption of aeration processes in the soil:

  • oxygen becomes less;
  • bacteria die;
  • toxins and poisons remain in the aquarium.

The average rate of growth of detritus depends on the size of the aquarium and the type of plants in it. The soil can silt within six months, or it can remain clean for a year.

The algorithm of actions of the owner of the aquarium depends on the state of the bottom filler:

  1. If the soil is completely covered with detritus, it is necessary to clean it with a siphon over the entire surface, with the exception of planting sites. Silt is a substrate for their growth and development.
  2. In case of excessive silting after cleaning with a siphon, you should change the water by a quarter. You can continue to replace once a week for 1-2 months, focusing on the condition of the soil and water.
  3. In neglected and neglected aquariums, a complete replacement of soil and water is acceptable.

Unsuitable plants

Unusual plants decorate the aquarium, but the selection of aquatic flora requires special knowledge. Improper planting can lead to rotten eggs and sewage smell in the following cases:

  1. Little space: you need to remove some of the plants.
  2. The natural specific smell of vegetation: such algae are completely removed.
  3. Lack of plants with a large number of putrefactive microorganisms: it is necessary to plant new vegetation and ensure high-quality filtration.

The death of a plant and its subsequent decomposition can also become a source of smells like rotten eggs and sewage. In this situation, you need to remove the remains of the plant and replace or change the water, depending on the degree of contamination.

Untimely cleaning

An important aspect of aquarium care is regular and gentle cleaning . With untimely cleaning, the plants become covered with mucus, plaque appears on the walls of the aquarium, the water becomes cloudy and fetid.

It is necessary to strive for such a ratio of water, plants and animals, in which the aquarium ecosystem copes with purification on its own.

Intervention in the life of a properly organized aquarium in the form of a full-fledged cleaning can be minimal, up to 1 time per year. In the intervals between general cleanings, it is enough to monitor the operation of the filters and process the soil with a siphon.

In the case of a running aquarium, it is impossible to do without global cleaning. It includes:

  • washing the soil and decorations;
  • cleaning the walls of the aquarium;
  • removal of overgrown plants;
  • filter cleaning.

To maintain cleanliness, it is important to regularly refresh the water, scooping out a quarter and adding the same amount of clean and settled water. You can also add cleaner fish and snails to the aquarium.

A large amount of soil

Soil plays an important role in the life of the inhabitants of the aquarium. In addition to creating beautiful scenery, it copes with the following functions:

  • substrate for aquatic plants;
  • creating suitable conditions for the development of microflora in the aquarium;
  • water purification.

However, in excess, it is prone to acidification due to the increased reproduction of bacteria.

At the same time, the retaining properties of the soil turn from a virtue into a disadvantage, because food residues accumulate in its layers, the aquarium becomes contaminated faster than usual, and the rate of reproduction of bacteria and the amount of gas they produce increase.

Reducing soil volumes is a logical solution to the problem, but first you need to determine:

  1. Water condition. It may need to be refreshed or replaced.
  2. The optimal ground height, which depends on:
    • type of filler;
    • the size of the aquarium;
    • number of fish and plants.

Soil, selected correctly and in the right amount, will not turn sour and spoil the water in the aquarium.

How do prevent Rotten Eggs And Sewage Smell in a fish tank?

how do prevent rotten eggs and sewage smell in a fish tank

The following recommendations will help you understand when fish and other pets need help:

  1. You need to keep an eye on the inhabitants of the aquarium. Unusual behavior, loss of appetite, excessive slowness are warning signs.
  2. Use high-quality filters in which you can adjust the flow rate of water. Check the condition of the sponge inside the filter.
  3. Aeration must be optimally adjusted.
  4. Buying soil, plants, fish, and other inhabitants requires some knowledge. You can not fill the aquarium at random.
  5. To prevent the water from becoming rotten again, follow the recommendations regarding feeding and cleaning.


The fish tank smells like rotten eggs and sewage is a common problem. It is decided depending on what circumstances contributed to its occurrence. Following the recommendations and following the rules will help minimize the risk of water damage again in the future.

Leave a Comment