Total Alkalinity for Hot Tubs

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Ideal Total Alkalinity Range for Hot Tubs: 80-120

Testing Hot Tub Alkalinity: Test your hot tub’s alkalinity level at least twice per week, with a test kit or strips. We also recommend taking a water sample to a dealer test station periodically (once per month) to verify results.

If using a FROG® System, use only FROG® Test Strips to help you dial in the low chlorine or bromine level used with FROG minerals. With standard test strips you could over brominate which wastes money. Using FROG Test Strips can help your bromine cartridges last up to 50% longer!

What is Total Alkalinity?
Total Alkalinity describes how “buffered” the water is against sudden changes in your hot tub’s pH. The alkalinity of your hot tub is perhaps the most important water balancing step in your hot tub to manage and should always be the first thing you test before adding chemicals, including FROG® products, into the hot tub. The ideal range for your hot tub’s alkalinity level should be between 80-120 ppm (parts per million). If you are unsure if your water is adequately balanced, our Langelier Saturation Index (LSI) calculator can tell you.

Note: You can have technically balanced hot tub water, as measured by the Langelier Saturation Index (LSI), even if your total alkalinity levels may be a little high or low.

Low Total Alkalinity

Just as low pH and low calcium hardness levels can be damaging to your hot tub, so can having a low total alkalinity level. While a low alkalinity level may not immediately be noticeable on hot tub equipment and surfaces, a low alkalinity level will often drive the pH level in the hot tub down, turning the hot tub water more acidic, resulting in itchy dry skin and irritated eyes. Additional problems associated with a low total alkalinity level in hot tubs include:

  • Pitting, etching, cracking and delaminating of hot tub walls and surfaces
  • Corrosion of metal surfaces in or around your hot tub (i.e. heating elements, pump seals, internal parts on gas fire heaters, pipes, etc.), which can also result in stained hot tub walls
  • Hot tub sanitizers (i.e. chlorine particularly) are less effective, so to achieve the same sanitizing effect you’ll need to add more
  • pH bounce (when a hot tub’s pH level quickly fluctuates up and down

How to Raise Alkalinity in a Hot Tub
Before you begin to adjust the total alkalinity in the hot tub, be sure you know how large your hot tub is (gallons) and what your target range is. You ideally want to be in the middle of the range between 80-120 ppm. If you are unsure of how big your hot tub is, our Spa Volume Calculator can help.

There are two ways to increase your hot tub’s alkalinity level: sodium bicarbonate (baking soda) or any type of alkalinity increaser product. If you choose to purchase an alkalinity increaser product be sure the product is made from sodium bicarbonate, which is the main substance used to raise pH. As always, after adding the alkalinity increaser or baking soda, let the hot tub sit for at least 6 hours before retesting.

High Total Alkalinity

While high alkalinity levels are not as damaging to your hot tub as low alkalinity levels, it’s still important to keep the Total Alkalinity balanced to prevent against unplanned maintenance costs and prolong the life of your hot tub filter, pipes and other equipment. The most common problem hot tub owners experience with high alkalinity levels is cloudy/ murky water, as hot tub water with high alkalinity allows for particles to more easily come out of solution (i.e. substances float freely in the water). It is from this dissolution of water that many of the other hot tub issues associated with high alkalinity stem, including:

  • Water scaling on hot tub surfaces and equipment
  • Reduced water circulation due to clogged pipes and filters as particles come out of solution, floating freely in the water and are deposited on things the hot tub water comes in contact with (i.e. scaling)
  • Clogged filters
  • Higher water pressure, as pumps become clogged and pipes narrow with scale they are forced to run harder, resulting in cracks and reducing their lifespan
  • pH lock, where changes to the hot tub water’s pH are resisted due to the high alkaline level in the hot tub

How to Lower Alkalinity in a Hot Tub
The two most popular chemicals available to help you lower the Total Alkalinity in your hot tub are muriatic acid and sodium bisulfate (also known as dry acid). After you’ve added muriatic acid, dry acid or another alkalinity decreaser product, be sure to check the pH level in the hot tub, as the pH level may have dropped as well.

Simplify your hot tub water care! FROG Fresh Mineral Water Systems kill bacteria two ways with minerals and a low level of bromine for ultra clean water. FROG also helps maintain pH levels to keep your water balanced.