What Causes High pH in a Saltwater Pool? (2 Simple Reasons)



Is the pH in your saltwater pool always high?

Are you having trouble figuring out why the pH is constantly on the rise despite your efforts to keep it down?

This article will cover the two reasons salt pools tend to have a higher resting pH, the most common causes for high pH in a saltwater pool, and how to go about fixing it.

Why Saltwater Pools Have a High Resting pH

The usual advice when it comes to the pH level for your pool is to keep it anywhere between 7.2 and 7.8.

Saltwater pools, however, tend to sit at the upper limit of that range (or even slightly higher) regardless of how many times you try to “rebalance it”.

Here’s why:

1. You’re Not Using Chlorine Tablets

Most traditional chlorine pools typically run on chlorine tablets to sanitize their water.

These are usually trichlor.

Trichlor tablets are very acidic with a pH level of around 3 – so, as they dissolve, they lower the pH of the pool water resulting in a small but continuous downward pull on the pH.

Saltwater pools aren’t subjected to this; they make their own chlorine, so they don’t need chlorine tablets like traditional chlorine pools.

Without the constant downward pull of a slowly acidic substance, the water in a saltwater pool naturally sits a little higher on the pH scale.

2. Your Saltwater Generator Makes Bubbles

Sounds silly, right? How can bubbles cause your pH to go up?

Spoiler alert: They do.

It has everything to do with your saltwater generator, which is tasked with converting salt into chlorine.

But this process has an unintended consequence. As salt is converted into chlorine, the generator produces a byproduct of hydrogen gas that bubbles on the surface of your pool water. This bubbling releases carbon dioxide from the water.

Like the trichlor tablets mentioned above, dissolved carbon dioxide is acidic.

And, in much the same way, if you remove an acidic compound from the water, it becomes more basic, causing the pH of the water to increase.

Note: This bubbling effect is called aeration and it’s often used to deliberately raise the pH of pool water.

Other Causes for High pH in Saltwater Pools

Saltwater pools function much like traditional chlorine pools.

For that reason, many of the causes for rising pH in a chlorine pool also apply to saltwater pools, which can take your pH level even higher.

To summarize, these are:

  • You shocked your pool. The most popular shock treatment is calcium hypochlorite with a pH level of 12, so using this on a regular basis is slowly going to raise the pH of your water over time.
  • You accidentally used a pH increaser. Household products like baking soda and borax are sometimes used as pool cleaning agents. They also have a high pH and are commonly used in pH increasers.
  • You used high pH water. If you filled or topped off your pool with alkaline water, whether it’s city or well water, you’re going to see an increase in the pH of your pool water.
  • You have pool algae. Algae consume carbon dioxide in the water; an acidic compound that pulls the pH of your pool water down. As more of this is removed from the water, the pH naturally drifts upwards.
  • You have water features. Similar to the bubbling effect caused by your saltwater generator, water features are aerators that dispel carbon dioxide from the water and ultimately cause pH to rise.
  • You replastered your pool. If your water has a low LSI, it will begin to suck calcium hydroxide from curing plaster in order to satisfy calcium demand. Calcium hydroxide has a pH level of 12.

How to Lower pH in a Saltwater Pool

While saltwater pools tend to sit higher on the pH scale, a reading of more than 7.8 is still considered too high.

The same methods used in traditional chlorine pools can be used to lower the pH in a saltwater pool.

The most popular option is to use muriatic acid (hydrochloric acid). Muriatic acid comes in liquid form so it can be a little daunting to handle at first, but this can be offset by wearing the appropriate safety equipment.

With that being said, it’s very efficient at lowering pH with the fewest side effects on your water, largely because it doesn’t contain other unnecessary and potentially harmful chemical compounds. It’s also the most cost-effective acid in most regions.

Another option is to use dry acid (sodium bisulfate). Dry acid comes in powder form so it does tend to be easier to handle, which also makes it notably safer to use.

The problem with dry acid is it adds sulfates to the water, which are very difficult to remove without using expensive reverse osmosis or draining and refilling.

A high concentration of sulfates will cause damage to paster surfaces and other pool equipment. In fact, saltwater pools are particularly vulnerable because sulfates also corrode the metal plates of a saltwater generator, reducing its lifespan.

Bottom line: Use muriatic acid in your saltwater pool.

Salt Pools Are Pretty Basic

Yes, salt pools tend to have a higher pH than traditional chlorine pools.

This is not only because they lack chlorine tablets, but also because of the aeration caused by saltwater generators.

Fortunately, once you understand how these differences affect your water, maintaining a suitable pH level in a saltwater pool is perfectly doable with a measured dose of acid and a little chemistry know-how.

Categories: Pool Care, Pool Chemistry