Why Does My Hot Tub Smell Like Fish?

Jennifer Rhodes

By Jennifer Rhodes · Updated

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Do you ever open your hot tub and smell something strange? Not the clean, bubbling oasis you were hoping for but something a little more... pond-like?

If your hot tub smells like fish, it's likely because there is a build-up of bacteria in the water. This can happen if the hot tub is not cleaned regularly, or if the filter is not changed often enough. Fishy smells can also be caused by a problem with your sanitizer or pH level.

This is a really common problem, but don't worry, we're going to tell you why it happens and how to fix it!

How to troubleshoot the problem

There are a few things you can do to figure out why your hot tub smells like fish. Here are the three most common causes:

1. Not enough sanitizer

If your hot tub smells like fish, it's often because there's not enough sanitizer in the water. Sanitizer helps to kill bacteria and other contaminants that can cause bad smells, so it's important to maintain the proper levels.

There are a few different types of sanitizer that can be used in hot tubs, but chlorine is the most common. You can purchase chlorine tablets or granules at most pool supply stores, and adding the recommended amount to your hot tub will help to keep it clean and smelling fresh.

Check your sanitizer level using some test strips, and shock your spa until your chlorine or bromine is in the correct range.

Poolmaster 22211 Smart 4-Way Swimming Pool and Spa Water Chemistry Test Strips
Poolmaster 22211 Smart 4-Way Swimming Pool and Spa Water Chemistry Test Strips
View on Amazon

If the smell persists even after adding more sanitizer, it's possible that there's something else causing the problem.

2. pH is out of range

If your hot tub's pH is out of range, it can cause a number of problems. High pH levels can make the water feel slippery and can cause irritation to the skin and eyes. Low pH levels can cause the water to become corrosive, which can damage the hot tub and its components, and—you guessed it—low pH can also cause a fishy smell.

To determine whether pH is the cause of your hot tub smelling like fist, check the pH level of the water with some test strips or a more advanced kind of test kit.

To fix an out-of-range pH, you'll need to adjust the levels using a pH increaser or decreaser. This can be done by adding pH up to raise the pH level or pH down to lower it. Once the pH level is back within the normal range (7.2 - 7.8), the hot tub should function properly and any fishy smell should go away.

3. Bacteria or algae growth

Another common cause of a fishy hot tub is bacteria or algae growth. Bacteria thrive in warm, moist environments, so hot tubs are a perfect breeding ground for them. Algae can also grow in hot tubs, and while it is not harmful to humans, it can cause the water to smell fishy, or like a pond.

To get rid of bacteria and algae, you will need to shock the hot tub with chlorine or another oxidizing agent:

Non-Chlorine Spa Shock for Hot Tub by AquaDoc
Non-Chlorine Spa Shock for Hot Tub by AquaDoc
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You should also clean the filters and circulate the water regularly to prevent the growth of these organisms. A dirty filter can cause bacteria to build up, which can lead to a fishy smell.

How to prevent the fishy smell coming back

There are a few things you can do to prevent your hot tub from smelling like fish in the future.

  1. First, maintain your sanitizer at an appropriate level. You’re aiming for 1-4 ppm for chlorine, and 2-6 ppm for bromine.
  2. Test the pH at least weekly, and then add either pH up (alkaline) or pH down (acid) until it’s within the range of 7.2-7.8.
  3. You should also drain and refill your hot tub every 3-6 months, replacing the old water. Thoroughly clean the hot tub shell while it's empty as part of this process.

I have a free printable hot tub maintenance schedule which you can download to remind you of exactly what to do.

By following these simple tips, you can help keep your hot tub smelling fresh and fish-free.

Closing thoughts

If you have a hot tub that smells like fish, it is likely because there is a build-up of bacteria in the water. This can be caused by a number of things, including low sanitizer or pH, not changing the water often enough, or not cleaning the filter regularly.

To get rid of the fishy smell, you will need to test the water to figure out the cause of the issue. Then, you can correct whatever is out of balance to fix the problem. You should also replace your filter if it's been in there a while, and consider draining and refilling the tub if the problem persists.

If you've tried all of these troubleshooting tips and the hot tub still smells like fish, you may need to call a professional to take a look at it.

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