When people ask me for advice on their swimming pools or spas on where they should start at the beginning of the season, I tell them that the most important critical parameter test to run for water treatment is the total alkalinity test because low or high alkalinity can make or break your pool water chemistry. How do you Lower Alkalinity Without Lowering pH?
Running pool features, bubblers, sprayers, jets, & waterfalls, create turbulence that will remove CO2 faster raising the pool’s pH & when total alkalinity needs lowering without affecting the pH level, an acid is added, & the pool water is aerated to raise the pH level without affecting alkalinity.
The longer you operate a swimming pool the more you can how water chemistry works and the more you learn about how water chemistry the more money and time you can save and that’s a good thing.
How to Lower Alkalinity Without Lowering pH
Total Alkalinity (TA)
is the sum of dissolved alkali in the water; specifically, substances that can take Hydrogen ions (H+). The ability to take Hydrogen slows the drop in pH, hence alkalinity is a measure of the pH buffering capacity of water that resists a drop in pH. The opposite of alkalinity would be acidity, which resists the rise in pH
Total alkalinity and pH are so closely related that lowering alkalinity without lowering pH is pretty challenging, but not impossible. Adding an acid to water will lower the total alkalinity, but it will also lower the pH levels somewhat.
If the total alkalinity needs lowering without affecting the pH level, an acid is added, and straight after the water is aerated to raise the pH level without affecting the alkalinity. However, in reality, you cannot lower or raise one without it affecting the other.
When reducing alkalinity with acid most time pH will also be reduced. But there is a way to minimize this: create turbulence in the pool so CO2 leaves as fast as possible. This means accelerating the loss of CO2 so the pH rises back up and leaves the pool water quickly.
This means running water features, bubblers, sprayers, jets, waterfalls, and anything else you can. We have seen people get creative with air compressors and diffusers to create bubbles. The point is, you want the CO2 out faster.
What Causes Low Alkalinity in Pools?
- Rain can be acidic
- Increase in swimmer load
- Topping your pool off with H2O that has low alkalinity-after backwashing/wasting
- Chlorine-Chlorine is acidic
- High H2O evaporation-losing H2O can dilute TA
- Pool H2O agitation-H2O agitation increases the loss of CO2 affecting TA
- Lotions & detergents-Keep a pool shower ……………………………………………………………………………………. Read more
Controlling pH
Technically the pH is the concentration of Hydrogen ions, expressed logarithmically between 0-14. But that’s complex and hard to wrap our heads around. So for practical purposes, a better way to understand pH is by thinking about the amount of carbon dioxide (CO2) dissolved in your water.
The more dissolved CO2 in your water, the lower the pH, and vice versa. This should explain why CO2 injectors lower pH, and why aeration (such as splash features, spillovers, and spa jets) raises pH.
If you’ve got water, any gas dissolved in that water has to be the exact proportionate pressure of that same gas above the water. And it’s not necessarily equal, it’s proportionate. In this case, the gas we really care about is carbon dioxide. Why CO2?
How do you adjust High pH with High Alkalinity?
- Run pool pump-bypass filter
- Test Total Alkalinity
- Calculate Muriatic Acid addition with a Pool Alkalinity Calculator
- Mix Muriatic Acid in a bucket of pool H2O
- Evenly distribute by walking around the perimeter of the pool
- Wait for 6-8 hrs
- If TA is 80-130 ppm.……………………………………………………………………………………Read more
Because the amount of CO2 is going to help you determine the pH. The less CO2 in your water, the higher your pH. The more CO2 dissolved in your water, the lower your pH, because you’ll have more carbonic acid.
If you have waterfall spray features, splash features, vanishing edge, aeration of any kind, bubbles, whatever. Your pH rises in those pools pretty quickly. The reason for that is those bubbles accelerate the loss of CO2. Your CO2 leaves, and your pH goes up.
If you want to reduce pH, you can inject CO2. The pH goes down, but the alkalinity doesn’t. And the reason the alkalinity doesn’t is because you didn’t do anything to the alkalinity.
If you need more CO2 to lower your pH, how does HCl find CO2? Well, it takes it from alkalinity. The way I describe it and it’s not chemically accurate, but it’s a good visual. Is it burns through alkalinity? The acid will burn through alkalinity, convert it to carbonic acid, and boom. Your pH goes down.
The amount of carbon dioxide in water determines the pH of the water. The more CO2, the lower the pH, and vice versa. A pool’s pH will naturally rise over time, thanks to CO2 leaving the water.
Henry’s Law of solubility of gases explains why CO2 leaves until it is in equilibrium with the atmosphere. When that equilibrium is reached, the water is at what we call its “pH ceiling”. This ceiling is determined by the carbonate alkalinity in the pool water.
Does Rain Lower Pool Alkalinity?
Yes-but taking a defensive approach, a pool owner can ward off the effects of added acidity, phosphorus & organics affecting the chemistry in a well-balanced pool before it rains by building the pool H2O up:
- Alkalinity levels up to 20-30 ppm
- Raising pH up to the 7.6-7.8 range
- Raise Chlorine Levels
- Run Pool Filter ………………………………………………………………………….. Read more
JimGalloway Author/Editor
