How often do you need to change the hot tub water? - Sutro, Inc

How often do you need to change the hot tub water?

So, you have a wonderful hot tub that soothes the senses with sparkling warm water. A weekly dash of pool shock keeps the water clean, and you follow the hot tub maintenance schedule. 

But did you know that the water sometimes needs to be replaced with fresh water? 

Yes, the water needs to be changed, and it is simple math and inspection rather than guesswork. 

Read further and find out how often you must change the hot tub water.

Why do you have to change the water? 

The answer is simple - it gets dirty! 

The water in your hot tub churns over and over and collects all the particles and chemicals you add for maintenance. The shield between clean and dirty water is the filtration system and the sanitizer. However, they have limits. 

Then the quantity of water in the hot tub is fixed, and the repeated addition of chemicals and contaminants saturates the water and increases the TDS (Total Dissolved Solids). This phenomenon is known as supersaturation. 

When the water is supersaturated, adding more chemicals does not work. Plus, this water can start creating problems like scaling on the surfaces and inside the hot tub. And can eventually result in a maintenance issue or possibly a complete breakdown. 

If the water goes unchanged for long periods with all this supersaturation building up, your hot tub will eventually look like a gunky water hole. 


How often should you change your hot tub water? 

Changing the water in your hot tub will depend upon several factors. It can be a date on your calendar when following an informed schedule or a culmination of visible contamination.

The Simple Math 

Perhaps you are unaware of it, but there is a simple formula to calculate the frequency of changing hot tub water. It considers the pool volume and the number of users daily. 

Say you have a 450-gallon hot tub used by two people daily. So, according to the formula, 450 is divided by two, and the result is then divided by three. That gives you the number of days (75 days in this example) after which you should change the water. 

Formula: 450 gallons (hot tub water) / two (daily user) / 3 = 75 days

Regularly Cleaning the hot tub filtration system can significantly extend this period. Also, habits like taking a shower before entering the hot tub to remove soap, lotion, makeup, etc., are helpful. 

Regular Checks

Another method to learn about the frequency is to conduct regular water chemistry tests. If water chemistry levels have gone berserk and you don't have time to balance the water, then sometimes it's easier to drain and refill if you are in a hurry. 

An easy method to keep an eye on the water chemistry is to use the Sutro Water Monitor, which provides real-time data on your chlorine or bromine levels along with pH and alkalinity. The Sutro mobile app lets you know if your tub is ready to use. 

Visual Signs

The buildup of biofilm (white water mold or algae) is easily visible and calls for a chemical treatment. However, if the water is too cloudy or foamy and stinks, the best route is to drain the hot tub. Other situations, like spilling liquids in the water or fecal contamination, may also require a change of water. 


The general rule says you should change the hot tub water every three to four months. This frequency can increase or decrease based on the usage of the pool. You can either use a simple formula to calculate the frequency or look for visual signs that call for a complete refill. The key to maintaining a clean and clear hot tub is frequent testing and keeping the water balanced. 

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