How to Lower the Alkalinity in Your Above Ground Pool

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How to Lower the Alkalinity in an Above Ground Pool
Image credit: Chris Grazioli, Flickr

What is water alkalinity?

Water alkalinity tells you how much of the acid in your pool can be neutralized to keep things functioning correctly. It should stay between 80-120 ppm.

Why does it matter?

High alkalinity reduces the ability of chlorine to sanitize your water. It also causes high pH levels, the acids, that are challenging to get under control. High pH causes high calcium build-up, which causes your water to get cloudy or turn green. It can also create a hard crusty build-up on the top of your pool that’s called scale.

High alkalinity can also be uncomfortable for people using the pool. It can cause your eyes to burn or make your skin itchy.

Two ways to lower total alkalinity

Lowering alkalinity can be done by adding chemicals to your water. Before you put anything in the pool, though, double-check how much water your pool holds. The amount of chemicals to use depends on how much water you have. The two compounds that you can use are muriatic acid and sodium bisulfate, or dry acid.

1. Muriatic Acid

Muriatic acid is slightly diluted hydrochloric acid.

WARNING: This acid will burn your skin and eyes. Be sure to wear rubber gloves, long sleeves, and goggles whenever you are using it.

  1. Test the water to determine that your alkaline level is high, and by what percent.
  2. Turn the pump off and let the pool sit for about an hour, so the water is absolutely still.
  3. While you’re waiting, read the back of the muriatic acid bottle to see how much you need to add for the amount of water in the pool and the percentage that your alkalinity is over what it should be.
  4. This acid can be poured directly into your pool, or you can dilute it first if you prefer.
  5. Walk around your pool, pouring the acid in many different spots. Make sure that the stream is narrow and heavy enough to reach the bottom.
  6. Let the chemicals sit in the still pool for one hour.
  7. Turn your pump back on to allow it to circulate again.
  8. Recheck your chemical levels after six, but before 24 hours from the time that you added the chemicals.
  9. Levels may not always drop immediately. If they’re still high two to three days after treating, repeat the treatment. It may take a few days for things to level out.
muriatic acid
Image credit: Morgan Davis, Flickr

2. Sodium Bisulfate (dry acid)

  • Sodium bisulfate is typically 93.2% pure, so make sure it’s labeled that way before purchasing it.
  • Test the water to see what percentage the alkalinity level is over the recommended amount.
  • Turn the pump off and let it sit for an hour, so the water becomes completely still.
  • While you’re waiting, read the label on the back of your product to determine how much you need to add.
  • Pour the dry acid into a bucket of water and let it dissolve completely.
  • Pour into the deepest part of your pool that you can reach.
  • Make sure that you have a steady stream when pouring, so it will penetrate the top of the water and reach to the bottom.
  • Allow the pool to sit for one hour, then turn your pump back on.
  • Retest the water after six hours.
  • If your levels are still high, you can repeat the process. Alkalinity levels can take a while to decrease, so you’ll want to wait two to three days before repeating the process.
    Sodium Bisulfate
    Image credit: Teravolt, Wikimedia


The chemical levels in your pool will determine how all parts of it will perform. If they’re maintained correctly, your pool should last for years. If not, you can expect liners to break down, hoses to clog, or filters to become plugged. Any of these can and will shorten your pool’s life drastically. Read up so that you know what each chemical is, what the safe levels are, and how to keep them there.