How Can You Treat Stinky Aquarium Water?

Fishbowl and an aquarium on a sideboard
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Unless you stick your nose in the filter, most aquariums are relatively odor-free. Occasionally, an aquarium owner will report that they have been stricken with unusually stinky aquarium water. Anytime you can find the aquarium using only your nose, there is something decidedly wrong, and quick attention is indicated.

Causes of Odors

  • Dead Fish
  • Excess Food Decomposing
  • Excess Fish Wastes
  • Decomposing Plants

    The most common cause of a smelly tank is a dead fish. It may be several days following the death of the fish before the owner realizes something is amiss. The fish may have jumped out of the tank, or it may have hidden in an out of the way corner of the aquarium. Either way, as the body decomposes, an odor is possible. Promptly locating the body and removing it should eliminate the odor.

    Overfeeding is another common cause of stinky fish tanks.  The uneaten food falls to the bottom of the tank, where it promotes overgrowth of bacterial colonies. As the bacteria grow exponentially, gasses are released, causing a foul odor. Pretty soon it’s a veritable swamp of decaying and stinking, organic material.

    Excessive fish waste can also be the cause as the result of overstocking the tank. When fish eat, they produce waste and the number of fish increase, so does the waste. Eventually, the overabundance of waste is too much for the filters and beneficial bacteria to process.

    What to Do

    The first thing to do is take an inventory of your fish. Are any missing? If so, start searching for the remains, as that may be the cause of the bad odor. Be aware that sometimes fish are consumed by their tank mates, so a missing fish may never be found. Despite this, you should know how many fish you have, and be able to determine if one, or more, are missing.

    If a decomposing fish body is not the source of the odor, the problem is an excess of organic material. The source of that could be uneaten food, dead plants, or simply too much fish poop. The first two items are relatively easy to determine by examining the tank for plant remains, and particles of uneaten food. If there is a lot of debris on the substrate, odds are you are overfeeding.

    Give the tank a good cleaning, and then cut back the feeding regimen to one small feeding per day. It may also be necessary to clean the filter, as generally when there is a lot of debris in the tank, the filter is clogged and not doing a good job of filtering the water.

    Preventative Steps

    Once you’ve eliminated the source of the problem, there are some steps you can take to ensure the problem doesn’t come back.

    Never forget that what goes in the tank stays there. Overfeeding is the number one cause of many aquarium problems, including smelly water. Feed your fish sparingly. Unless you stop feeding your fish entirely, they are not going to die of starvation. Fish can, and will, suffer a variety of disorders if they are overfed. 

    Make sure you do regular water changes and tank cleanings. Aquariums are a closed environment, so cleaning is an absolute must to ensure a healthy, and stink-free, environment.

    Sometimes odors are the result of a slow rise in waste by-products, due to never performing a water change. When doing your regular maintenance, don’t forget the filter. Using carbon media in your filter to help reduce odors, but it has to be changed regularly to be effective.

    Bottom line, keep it clean, and you won’t have problems. A well-maintained aquarium is not likely to ever develop an overpowering odor.