Most hot tub and pool owners are aware that they need to maintain a proper pH and alkalinity in their water, but few people actually know why. In this post I will go over what pH and alkalinity are and why they matter.

What is pH?

pH stands for “potential of hydrogen” and is the measure of how many hydrogen (H+) ions are present in water. The less hydrogen ions there are in the water the more acidic the water becomes. pH is measured using the pH scale you’re familiar with from science class where 7 is neutral, 0 is the most acidic, and 14 is the most basic (also known, confusingly, as alkaline). This scale is logarithmic and not linear; meaning that as you go from one number to the next you increase or decrease acidity by a factor of 10 and not one. (For example, water with a pH of 6.0 is 10 times more acidic than water with a pH of 7.0).

What is alkalinity?

Total alkalinity of water is a measurement of how much acid the water can neutralize without changing the pH. As things are added to the water that could raise or lower it’s pH, alkalinity will act as a buffer and prevent sudden shifts in pH. It is measured in ppm (parts per million). The higher the ppm, the more buffering ability the water has, and the less the pH will be affected by highly acidic or basic substances being added to the water.

What causes changes in pH and alkalinity?

The short answer is basically everything and everyone that goes in to the water. Everything has its own pH and alkalinity. If you add something to the water (Including humans. Our skin is fairly acidic with a pH of around 5.5) that is acidic/basic or has low/high alkalinity you will lower/raise the overall pH or alkalinity of the water.

pH in Hot Tubs and Pools

So how does this relate to pools and hot tubs? There are four main things that pH will affect; bather comfort, water clarity, chlorine efficiency, and the longevity of the equipment. Equipment in this case refers to pumps, heaters, filters, o-rings and gaskets, pool liners, concrete pool finishes, hot tub jets, pillows, covers and basically everything else that comes in contact with the water.

Water with a pH of less than 7 will start to become more uncomfortable and will wear out equipment quicker (especially anything made of metal). Water with a pH of more than 7.8 will also become uncomfortable, can become cloudy looking, cause scaling on surfaces of pools and hot tubs, and reduce chlorine’s effectiveness.

The pH of your eyes is slightly basic, sitting around 7.3-7.5. By keeping the pH in the ideal range of 7.4-7.6 you will greatly reduce the red, irritated feeling eyes that many people experience when swimming in unbalanced pools while also keeping your chlorine working effectively, keeping your water clear and getting a longer life from your equipment

Alkalinity in Hot Tubs and Pools

The ideal range for total alkalinity is between 80-120ppm in hot tubs and between 80-150ppm in pools, depending on the finish of the pool. Water with an alkalinity less than 80ppm won’t be able to buffer acids well; leading to rapid fluctuations in pH (tending to stay on the acidic side). Water with an alkalinity higher than 150ppm is buffering too well. The pH of the water will stay the same or raise despite pH reducers being added to the water. This can lead to the discomfort, cloudy water, chlorine inefficiency, and scaling that high pH brings.

Tips and Best Practices

  • Always adjust alkalinity before pH. Wait between 2-3hrs for a pool and 1hr for a hot tub after adjusting alkalinity before adding any other chemicals. This will give the alkalinity booster/reducer a chance to fully work and give you the most buffering ability before adding anything else.
  • Adding air to water will increase it’s pH. Turn your hot tub’s air controls off when you get out to prevent pH creeping up on you.
  • Make sure to regularly change the water in your hot tub (between 2-4 times a year, depending on usage) to keep the chemicals you add working at peak efficiency.
  • Make sure to get your water professionally tested at least once a month as the test kits at a pool or hot tub store are generally far more accurate than home test kits/test strips.
  • If your test kit is always reading low, the reagents/test strips may be expired. Bring a water sample to your local pool or hot tub store and see how the readings line up. If the water test results are higher than what you tested, it’s time to replace your reagents/test strips.
  • Is your water looking crystal clear? It might still need balancing; just as basic water can become cloudy, acidic water can be very clear, even if other problems exist.

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