Do Pet Fish Smell Bad?

Do pet fish smell bad? Truthfully speaking, it’s not your pet fish that smells bad!

The water, and bio-wastes, in your aquarium that haven’t been cleaned out, are actually what’s causing the odor. Stick around because we’re going to break them down!

Reasons Why Your Pet Fish Smell Bad

You shouldn’t blame the stench on your pet fish any longer, so here are some common reasons why there’s a foul smell coming from your aquarium.

1. Rot

The bad smell could be because something is rotting hidden somewhere inside your fish tank. It can be either of these three things:

  • Dead fish
  • Rotting plants
  • Fish food leftovers

Dead Fish

If you have a whole school of fish in your aquarium, it would be possible for an unnoticed fish to already be decomposing somewhere in the corners. A dead fish is actually quite smelly!

To spare everyone’s noses from this disaster, it would be best that you regularly do a head count. Always make sure that everybody’s present, alive, and swimming!

Rotting Plants

Another possibility is that there could be rotting plants. This should be the least common cause since it’s easy to spot any dying plants.

However, some owners don’t recognize these signs. In other cases, there are also those who hope that the plant will grow and come back to life again.

To prevent your plants from causing a nasty smell, promptly remove any decaying plants that no longer look like themselves. Dead plants tend to turn black or slimy brown.

Above all, properly take care of your plants and prune any rotting bits.

A green beautiful planted tropical freshwater aquarium with goldfish
A green beautiful planted tropical freshwater aquarium with goldfish

Fish Food Leftovers

It’s understandable that you don’t want your fish to starve. Still, overfeeding is never the solution.

Your pet fish will only eat so much, and a lot of the leftovers will be left ignored at the bottom of the aquarium.

This excess food will then rot and will most likely be another reason for your fish tank to smell.

Avoid this by observing just how much your fish can eat, then give the right amount (or a little over the right amount) when feeding.

Most importantly, maintain the cleanliness of your fish tank by removing all the excess food they couldn’t eat!

2. Dirty Filter

Filters are important equipment designed to absorb any dirt and smelly wastes inside the aquarium, so it’s natural for them to emit a foul scent.

All the organic matter it absorbed will become a mass of trapped gunk. Nevertheless, this shouldn’t be a problem when you regularly clean them.

Another important note, there are actually good bacteria in filters as well! So, only clean the filters during your scheduled cleaning days so as to not rinse away the good bacteria.

3. Water Problems

The next possible cause for the odor would be your aquarium’s water quality since it’s often affected by insufficient maintenance and chemical additives.

To prevent any undesired smell from emerging from your fish tank, avoid using water conditioners with high sulfur contents, which smell like rotten eggs.

However, if you could tolerate the strange smell, just endure it till the conditioner fully dissipates into the water. It will be like it wasn’t even there at all!

4. Fish Poop

When fish poop breaks down into the water, it will obviously cause bad odors. Never overstock and let the poop pile up to avoid this.

Regularly gravel vacuum the substrate to remove the fish poop, and this should help eliminate the poop smell after a few minutes.

How to Get Rid of the Bad Smell

We’ve given you quite a few reasons for the bad smell, and the only way to get rid of it is to clean, clean, clean!

Step 1: Identify the Problem

If you’re suddenly getting a whiff of a stench coming from your aquarium, start by identifying what’s causing it and immediately remove it!

Fortunately, we’ve already previously discussed some of the reasons for the bad smell. They should help you get rid of the odor quicker!

Step 2: Maintenance

Prevention will always be better than cure. So, here are a few regular cleaning chores that you should maintain.

  • Wipe the glass.
  • Vacuum the substrate.
  • Prune the dead leaves off.
  • Clean the decorations.
  • Clean the rocks.
  • Clean the inflow and outlet of your filter.
  • Rinse the trapped gunk from your filter.
  • Change water.

Step 3: Partial Water Change

Perform a partial water change on a daily basis. About 10-20% of the water should be replaced.

This helps in adding fresh and odorless water to your aquarium while also removing part of the water that may already have a smell on it.

Step 4: Add Carbon Filter (Optional)

Odors are gasses that were built up, and a carbon filter will absorb all of these bad smells!

Additionally, activated carbons are known to magically remove any discoloration from your fish tank, making the water clearer!

The drawback is that carbon filters need to be replaced at least once a month. If not, the bad smell will return again.

How Often You Should Clean Your Aquarium

There’s no question, it’s important that you clean your aquarium regularly! The ideal rate would be at least once every two weeks.

However, if you own quite a number of fish, and if they’re also messy, the best would be once a week!

In addition, it would be a good idea to vacuum every 2 days. This is because fish that are fed similar quantities of food regularly also poop with the same frequency.

Congo Tetra on Black Background


Ultimately, fish are odorless creatures. In fact, they don’t have sweat glands that would cause them to sweat or smell.

That’s why you might have already noticed how you asked if pet fish smell bad but were instead given a bunch of pointers about maintenance.

It’s because, we’ll reiterate, fish don’t smell! But the aquarium they live in does, so proper maintenance is the key point to preventing any bad smell.

Remember, avoid the build-up of waste through regular cleaning, and be free of any undesired smell!