The main cause of a smelly fish tank is something rotting or decomposing, but identifying what is decaying and how to prevent it is the challenge. For instance, a source of fish tank odor might be anything dead, such as a fish or plants or rotting food from overfeeding. Also, a buildup of excrement in the water or substrate or a dirty filter can cause problems.
The best way to eliminate the odor from a smelly fish tank is to first identify the source of the stink, clean the tank, and effectively condition the water. Select the type and number of fish carefully depending on the size of the tank. Maintaining clear aquarium water is the goal.
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Fish tank odor eliminator
The best fish tank odor eliminator is likely some sleuth work and a thorough cleaning. Take a head count and keep track of how many fish you have. If one is missing, check behind rocks and plants for decomposing bodies. Similarly, regularly look for dead or dying plants if your aquarium contains live foliage and cut off dying branches. Dead plants are brown or black and slimy and will impact water quality quickly. Note that algae is a plant and can also rot, contributing to a smelly fish tank.
If there is no single source of odor, you might have to clean the aquarium thoroughly, including the substrate covering the bottom. Empty the tank including the fish, wipe down all the glass, rinse the filter, and strain the substrate to remove excess excrement that is often the source of foul aquarium odor. Sometimes, partial water changes without removing all the fish are helpful too.
Preventing a smelly fish tank
Prevention is often the best medicine, and this is true with smelly fish tanks too. There are several ways to avoid buildup of material that decays and causes odor. First, avoid overfeeding your fish. Any food they can't consume accumulates in the substrate and eventually rots. Second, avoid overcrowding, which can create excessive excrement. Remove some fish or upgrade to a bigger tank.
Finally, add suckermouth catfish, also called pleco, to help clean the algae from the aquarium tank. Malaysian trumpet snails are avid eaters and are very good for aquariums with live plants because they consume dying leaves. These scavenging snails also burrow through substrate. Regularly using a gravel vacuum is another way to keep rotting material from building up.
Importance of clear aquarium water
Clear aquarium water is important not only to avoid odor but to maintain the correct pH and low nitrate levels in the tank. Adding water conditioner can help keep the water clear, but avoid brands with a high percentage of sulfur because of its rotten egg smell. Clean the filter each time you clean the tank and consider adding an activated carbon filter, which absorbs bad smells and makes the water clearer.
Frequent small water changes of less than 25 percent of the total tank volume will dilute cloudy water. When you clean the tank, also remove and scrub any plastic ornaments. Then, scrape the glass with an aquarium algae scraper. Only use this tool so that the surface of the glass isn't scratched. Never use chemical cleaners or even dish detergent because both are highly toxic for fish no matter how much you rinse. Maintaining the tank's clarity is the best defense against smelly fish tanks.