Hot Tub Water Testing

Test tube

Whether you’re a new spa owner or a seasoned pro, keeping hot tub water balanced can be tricky. The best thing you can do when learning about how to maintain your spa is know all the different elements that affect spa water, namely four things: sanitizer, alkalinity, pH, and calcium hardness and be familiar with how to test each one. Here's a quick guide to hot tub water testing for anyone who might need additional help or may just need a refresher. 


There are a few different ways you can sanitize your hot tub, namely bromine, chlorine, Spa Frog, and Biguanide. Here are the recommended levels for them:

Bromine residual = 2-6 ppm

Brominating concentrate = 3-6 ppm

Brominating tablets = 2-4 ppm

Chlorine residual = 3-5 ppm

*Side note: if your spa utilizes either an ozone generator or you use Spa Frog products, you may maintain the chlorine or bromine at the lower end of their respective ranges.


Total alkalinity, or TA, is a measure of the amount of buffering capacity in spa water which ultimately acts as a shock absorber for the pH. If TA is too low, the water turns acidic and corrodes equipment and surfaces. Low total alkalinity will also lower the pH and make both difficult to balance without the other being at correct levels.

If it’s too high, the water is alkaline and scale buildup and cloudy water is often a result. The pH will also drift up and will be difficult to adjust if your total alkalinity isn’t balanced.

Much like pH levels, total alkalinity is affected by several environmental factors like rain, acidic sanitizers, fill water, and other product applications. These can all affect your alkalinity over time. Check and balance your TA once every few weeks.

Ideal range for total alkalinity is from 125-150 ppm, which will vary based on your spa water temperature and type of sanitizer you use. If you’re using chlorine or bromine, levels of up to 200 ppm are acceptable. Cutoff for Biguanide spas is 170 due to the foaming tendency of the product.

High TA

To compensate for high total alkalinity, add pH Down over several days in order to lower it. Add until the pH drops to 7.2 at the lowest. You should be aiming to achieve pH levels between 7.4 and 7.6. As the alkalinity rises, so should your pH levels.

If the total alkalinity is high and continues to increase and the pH is low and doesn’t respond to pH increaser, the problem could be bicarbonate scale. This happens when trapped gases or poor ventilation in spas are reabsorbed into the water. This drives pH down and TA up. To balance successfully, move covers and ventilate as well as possible and then begin to adjust. Keep the area well-ventilated or the cover removed until the hot tub water has balanced once again. This may be necessary to do for several hours each day.


As previously stated, pH levels should be maintained between 7.4-7.6. This range allows the sanitizers to perform effectively, the spa surfaces and equipment aren’t being corroded from acidity, and bathers are comfortable as they soak. Never to be underestimated, pH is one of the most important aspects of hot tub water quality, even though maintaining it can be a challenge. Levels of pH can fluctuate greatly because of heat, aerated water, and lots of use can adversely affect it.

Test your sanitizer and pH levels several times a week. You can do this using test strips which provide a quick and easy read.


Calcium Hardness

Calcium hardness, or total hardness, is the amount of dissolved calcium (and magnesium in the case of TH) in spa water. Calcium helps prevent surface etching and equipment corrosion which occurs when the water becomes too acidic. If the amount of these minerals gets too high in the water, the minerals “fall out” of the solution and creates cloudy water and scaling.

Low Total Hardness:

If your hardness levels are too low, you’ll need to add a product like Spa Pure Hardness Increaser. Low harness becomes corrosive and will result in pitting on your surfaces and will corrode any metals it touches. This can result in water discoloration and poorly functioning pipes.

High Total Hardness:

If you test your fill water and it has a lower hardness residual then partially drain your spa and dilute it with new water to lower total hardness. If the fill water has a high TA, add Stain and Scale Preventer.

If you ever have any problems you can’t solve via internet research, remember you can always call your local spa maintenance professional. They’re always there to help!
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