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Why Does My Aquarium Smell Bad?

Why Is There a Smell Coming from My Aquarium San Diego, CA

First of all, there’s absolutely no reason to own an aquarium that isn’t clean and odor free! Following these basic rules given below will ensure your fish tank doesn’t stink, but…if you’ve noticed your fish tank is giving off a foul odor, you’re probably concerned—and with good reason. A smelly fish tank is likely a sign something is going wrong with your aquarium system, and you should investigate to figure out exactly what that problem is so it can be dealt with. The staff at Aquatic Warehouse, a reliable aquarium supplier, shares some common reasons a fish tank might stink and what you can do to eliminate the smell.

You’re Overfeeding Your Fish or You Missed the Tank

The number one reason an aquarium gives off a foul odor is because the person feeding the fish basically misses the opening of the aquarium. When you cannot see the top of the tank, it’s easy to spill or miss the opening with a portion of the food. Then the food becomes moist and just sits there, turning the ambiance of your room into an extreme case of low tide. If you’re overfeeding your fish, they won’t be able to eat all of the food that goes into the tank. Uneaten food is left to sit and rot, eventually giving off an unpleasant odor as it builds up. You’ll likely notice a film that appears on the tank’s bottom or walls as food particles stick to the surface. Watch your fish as they eat, and don’t give them more than they’re able to consume in 2-3 minutes (the 3 minute rule).

The Aquatic Plants Are Dying

Live plants are a great way to decorate a tank and keep the fish happy and healthy. However, when these plants begin to die, they can give off a noticeable, foul odor that spreads around the entire aquarium. Check your tank’s plants every week for dying leaves and prune them as necessary. If a plant has completely died, remove it from the tank and replace 20-25 percent of the water and replace the carbon in the filter.

The Tank Is Overcrowded

All fish expel waste, but a properly filtered and regularly maintained tank won’t smell for this reason. If your tank is overcrowded, the filtration system may not be enough to handle the excess waste, which could cause a foul odor to start coming from the tank. Usually the filter is too small to handle fish that have grown in size from when they were small. Make sure you only have the recommended number of fish for your aquarium size and that your filtration system can handle the waste for your specific tank.

The Filter Needs to Be Cleaned

As your filtration system works to keep your fish tank clean, the filter itself can become dirty. Fish waste, algae, uneaten food, and any other contaminants in the tank can become trapped in the filter, causing a foul odor to be pushed out into the air and the rest of the tank. This problem can be easily solved by routinely cleaning the filter and adding carbon like Boyd Chemi-Pure:


Each time you clean and maintain your tank, remove the filter and rinse out any of the gunk that has begun to build up. Rinse in the discarded water removed from the aquarium, never in municipal water because the chlorine will kill the good bacteria needed to make the filter work correctly by turning toxic ammonia into manageable nitrates. Again, a lot of aquariums have a filter that’s too small, so add another filter or get a bigger one. Just remember you need to keep the old filter running for 4-6 weeks to allow it to become colonized with the beneficial bacteria.

It’s important to have the right supplies to keep your aquarium clean and running smoothly so your fish can remain healthy. Whether you need a filtration system, dosing pump, beneficial bacteria, or any other necessary aquarium supplies, Aquatic Warehouse has got you covered. Stop by our store in Kearny Mesa today, or give us a call at 858-467-9297 if you have any questions.


Contact Information

  • Address: 5466 Complex Street Suite 204
    San Diego, CA 92123
  • Phone: (858) 467-9297
  • Email: sales@aquaticwarehouse.com
  • Working Days/Hours: Mon - Fri / 10:00 AM - 7:00 PM
    Saturday / 10:00 AM - 6:00 PM
    Sunday / 11:00 AM - 6:00 PM


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