What to do after a hot tub refill

A one minute tutorial


The water in your hot tub can easily be saturated because of organic material entering the water. This organic matter can consist of a lot of different things such as skin, fats, oils but also calcium or sand and many more. The water will at some point become irregulare to handle.

  • After you refill the hot tub, start with the water balance.
  • pH level is the significant factor concerning water balance.
  • pH level will let you know how acidic or basic the water is.
  • The pH level should be between 7.2 and 7.6 otherwise sanitizer can’t kill bacteria effectively… Adjust it up or down using pH + or pH –
  • ‍Add a Sanitiser and test the water again.


On average change filters at least once every year and make sure your water is not too old so you avoid saturation.
On average you need to replace the water every 3 months but it also depends on the intensity of use.
Start by checking the pH value and correct it if necessary by using pH + or pH -.
The pH level should be between 7,2 and 7,8 this will make sure that any sanitizer like chlorine or bromine can work properly.
This pH level will also ensure that the water itself will not be harmful to the equipment.

Next you should check what to do with the sanitizer.

Most commonly used is chlorine and bromine.

Important to know is that you want to know what the FREE chlorine level is because this is the chlorine that can still kill off contamination….Measurements for TOTAL Chlorine or COMBINED chlorine can be important but there is a difference.

We will explain further down but most test strips will only show FREE chlorine so you can start by correcting the value.
Add SANITIZER (chlorine or bromine). Ideal free chlorine between 3-5 ppm or ideal bromine between 2-6 ppm.
Chlorine will work quick and bromine takes more time to work.
To raise the level by 5 ppm in a 1500 liter hot tub you need to add about 15 grams to start.
To raise the level by 5 ppm in a 396 gallon hot tub you need to add about 0.53 ounces.


It is always difficult to advise in absolute numbers because different types of chlorine and different brands of chlorine can vary in the amount of active substance so always check yourself after mixing it.

Just to check your work after a mixing and see if the pH and chlorine/ bromine levels are good.

When and if you add O-Care the water can get cloudy…don’t worry that means it is working and it will clear up soon, sometimes minutes but depending on the water quality it can also take hours.

A headshot of Natalie Lapierre against a black background
Article by: Natalie Lapierre

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