Total Alkalinity for Hot Tubs

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Ideal Total Alkalinity Range for Hot Tubs: 80-120

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 measures how well your hot tub water resists sudden changes in pH. It’s one of the most important factors in maintaining balanced water and should always be the first thing you test before adding any chemicals — including FROG products.

The ideal alkalinity level for your hot tub is between 80 and 120 ppm (parts per million). If you’re not sure whether your water is properly balanced, try using our Langelier Saturation Index (LSI) calculator to find out.

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 start, make sure you know how many gallons of water your hot tub holds and what your ideal alkalinity range should be. The recommended range is 80–120 ppm (parts per million), with the middle of that range being ideal.
If you’re not sure how big your hot tub is, use our Hot Tub Volume Calculator to find out.

There are two easy ways to raise your hot tub’s alkalinity:

  1. Use sodium bicarbonate (baking soda) — a common household option.

  2. Use an alkalinity increaser product — just make sure the main ingredient is sodium bicarbonate, since that’s what actually raises alkalinity.

After adding your chosen product, let the water circulate and rest for at least 6 hours, then retest the alkalinity before making any further adjustments.

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

If your hot tub’s Total Alkalinity is too high, you can bring it down using either muriatic acid or sodium bisulfate (often called dry acid). These are the two most common and effective products for reducing alkalinity.

After adding your chosen product, always test the hot tub water’s pH level. Lowering alkalinity can also cause the pH to drop, so you may need to make small adjustments to balance both levels properly.

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.

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