All About Alkalinity


Alkalinity is one of the major components to balanced swimming pool water. Let’s take a closer look to what it is, what it does and how to adjust it.

Alkalinity is a close cousin to the pH. Often times you can relate alkalinity to the pH. In other words if the alkalinity is low then the pH is probably low too. Not always, but nonetheless it’s a rule of thumb you can use while you are out in the field.

Alkalinity measures how alkaline the pool water is. It measures things like carbonates, bicarbonates and things of that nature. According to the NSPF a swimming pool should have somewhere in the range to 80-120ppm in order to be considered balanced. I always tell my clients alkalinity is the guardian of the pH.

It directly affects the pH. If the alkalinity is low then you’ll get what is called “pH bounce” where the smallest change in the pool water will create a rapid change in pH. If the alkalinity is high then the pH will be resistant to change. That means it will take more of the chemical, applied in the proper way, to make the results occur.

You can really see how alkalinity is a buffer to the pH. What can a low or high alkalinity do to a swimming pool.

If it’s low…

  1. pH will become erratic
  2. Etching of the pool or corrosion to chrome pool equipment can occur
  3. Corrosive water conditions

If it’s high…

  1. The pH becomes difficult to adjust
  2. You can get cloudy water or scale formation on your pool surface and/or equipment
  3. Chlorine become less effective due to the higher pH

Either high or low can create swimming discomfort. If your alkalinity is low you can get itchy and irritated eyes. If the alkalinity is low you can dry eyes. So it’s really important to keep the alkalinity in range.

How do we adjust the alkalinity? Let’s start if it’s low.

If it’s low…

  1. Use sodium bicarb (baking soda) to raise it. You can apply it directly to the skimmer to eliminate the cloud effect from broadcasting it around the pool surface. It also does not dissolve well in colder water so that’s why it’s better to apply it through the skimmer.
  2. You can expect, per 10,000 gallons, to see a 10ppm change for every 1.4lbs (or 1.5 for easy numbers) applied in the pool. So if you needed a 20ppm change in a 20,000 gallon pool you would add 5.6lbs of bicarb.
  3. DO NOT add 10lbs at once. You will cause your equipment to become sluggish. If you have an undersized filter you need to add even less.

If it’s high…

  1. Use muriatic acid to lower it. This is done by applying it, in the deep end, with the pump off and in 1 spot. If you broadcast it you’ll be making a bigger change in the ph.
  2. Pre-dilute it first. Always add chemical to water and not the other way around. This will protect the pools surface from it sitting on one spot in the deep end.
  3. You can expect, per 10,000 gallons, to see a 10ppm change for every 24.6 ounces you add. So if you needed a 30ppm change in a 10,000 pool you would add roughly 75 ounces.

So there’s a quick down and dirty explanation on alkalinity for your swimming pool. If you have any questions please don’t hesitate to contact us.

Below is the Youtube video podcast discussing this topic.

Below is our podcast discussing alkalinity.

macbook onarim