How Do I Fix Low Alkalinity in my Pool?

Add sodium bicarbonate in small increments to raise total alkalinity levels to the ideal range of 80-120 ppm.

What Is Total Alkalinity and Why Does It Matter?

Total alkalinity measures the concentration of alkaline substances in your pool water. It acts as a buffer, helping to keep your pH level stable. Think of it as shock absorbers for your water chemistry.

Ideal alkalinity for most pools is:

• 80 to 120 parts per million (ppm)

When alkalinity drops below that range, even minor chemical changes or environmental factors (like rain or swimmer load) can send your pH into chaos.

Low alkalinity can lead to:

• Etching or corrosion of plaster, tile, and pool equipment

• Eye and skin irritation

• Cloudy water

• Difficulty maintaining a steady pH

What Causes Low Alkalinity?

Several things can cause your pool's alkalinity to drop:

1. Overuse of acidic chemicals: Adding too much muriatic acid or dry acid to lower pH can also lower alkalinity.

2. Rainwater dilution: Rain is naturally acidic. A heavy downpour can dilute pool water and shift chemical balance.

3. Source water: If your fill water is naturally low in alkalinity, topping off the pool regularly may keep levels low.

4. Heavy pool use: Swimmers, especially in commercial pools, introduce contaminants and shift water chemistry quickly.

Knowing the cause helps prevent it from happening again once you fix it.

How to Test for Alkalinity

Before you can fix low alkalinity, you need to know where it stands. Use one of the following:

• Test strips: Fast, easy, and give a ballpark reading.

• Liquid test kit: More accurate than strips and includes pH and chlorine levels too.

• Digital testers or pool store sample: Great if you want the most precise results.

If your reading is below 80 ppm, it’s time to take action.

Step-by-Step: How to Raise Alkalinity in Your Pool

Raising alkalinity isn’t complicated. The most common method uses sodium bicarbonate (baking soda), which raises alkalinity with minimal impact on pH.

Step 1: Calculate How Much Baking Soda You Need

Most pool experts recommend:

• 1.5 pounds of baking soda per 10,000 gallons of water to raise alkalinity by about 10 ppm

Example: If your pool is 20,000 gallons and your alkalinity is 60 ppm, and you want it at 100 ppm, you need to raise it by 40 ppm. That means adding about 12 pounds of baking soda.

Step 2: Add the Baking Soda

1. Turn on your pool pump to keep the water circulating.

2. Measure out the correct amount of baking soda.

3. Broadcast it evenly across the surface of the deep end.

4. Let the system run for at least 6 hours to distribute it thoroughly.

Avoid dumping it all in one spot or near the skimmer. Even spread is key.

Step 3: Retest After 6 to 24 Hours

Give the chemicals time to work, then test again:

• If the alkalinity is still too low, repeat the process.

• Once you're in the 80–120 ppm range, you're good.

What About Using Alkalinity Increaser?

You can also buy a product called alkalinity increaser at pool stores. It’s basically the same thing as baking soda, just packaged and labeled for pool use. It works the same way, but usually costs more.

How Does Alkalinity Affect pH?

Alkalinity and pH are closely linked, but they’re not the same. Alkalinity stabilizes pH, but changing one can affect the other.

When you raise alkalinity:

• pH may increase slightly, but usually stays manageable

• If pH rises too high, adjust it down slowly with a small dose of muriatic acid

Never try to adjust both at the same time. Fix alkalinity first, then test and correct pH if needed.

Tips to Keep Alkalinity in Range

Once you’ve got your levels right, here’s how to keep them steady:

• Test weekly using strips or a liquid kit

• Avoid overusing acid to lower pH

• After rainstorms, test your water and adjust as needed

• Add baking soda in small doses if alkalinity starts to drop

• Don’t ignore minor shifts, as they can snowball quickly

When to Call in a Pool Professional

If you’ve tried everything and your alkalinity still won’t hold, it could point to deeper issues:

• Poor water circulation

• Equipment problems

• Water source problems

• Incorrect pool volume calculations

A pool technician can run a full analysis and help rebalance your system. It’s worth the call if DIY fixes aren’t cutting it.

Fixing low alkalinity isn’t complicated, but it does require accuracy and patience. Once you understand how alkalinity stabilizes your pool, the fixes and prevention strategies become second nature. With regular checks and a few basic tools, your water will stay balanced, clear, and safe all season.