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Hot Water Chemistry: Basics

When it comes to your hot tub, it is important to test the water regularly to ensure safe swimming conditions and longevity of your hot tub. Hot water needs to be balanced properly, so lets take a look at the basics of hot water chemistry.


  1. Sanitizer - It is important to keep your spa properly sanitized. This could be either chlorine or bromine. A sanitizer ensures the water is clean, clear, and safe to use. It removes bacteria that could be living in hot water, too.

  2. pH - The natural state of hot water has a high pH, this is why testing your hot tub is so important! A pH range of 7.4-7.6 is recommended. You can adjust the pH in your spa by using pH down (to lower the pH) or pH up (to increase the pH.) When the pH in a spa becomes too low, it is unsafe to get in. A low pH means that the water is acidic and can burn the eyes and skin of those who get into that water. When a pH is low in a spa, it usually means it is time to completely drain the spa and start with a fresh refill.

  3. Alkalinity - This is the buffer for the pH, often times, alkalinity runs high in hot water too. It is important to keep your alkalinity in range in order to avoid drastic pH changes. The good news is, alkalinity is also lowered using pH down! So, if your pH and alkalinity are both high (which they probably will be) - then you only have to use one chemical!

  4. TDS- TDS stands for total dissolved solids, which is the concentration of every thing that is added to your hot tub. For example, when you fill your hot tub with hose water, the TDS may measure around 350. Over time, when you add your weekly chemicals, this number will grow... 400, 450, 500, and so on. Once this number gets to 2000, we recommend a drain and refill. If the water becomes too saturated (higher TDS) then your water could become cloudy, the chemicals will not work as effectively, and it can cause irritation to those who are in the hot tub.


All of the basics listed above are just the start to safe hot tub water chemistry. We recommend bringing in a water sample to our store once a week. When you do this, we are able to test the water for all of these values and more. With our test, we are able to tell you the exact chemical amount needed to get these values back into the safe range. In addition to a professional test once a week, it is also a great idea to have test strips on hand. You can use these before getting into your hot tub each time. A test strip will give you a general idea of where your levels are, so you know if the water is safe or not. A test strip will not tell you how much of each chemical to add to fix the values, but it will tell you if the sanitizer, pH, and alkalinity are within proper range!

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