What is Alkalinity in Pools & Hot Tubs and How to Fix it
First off, Alkalinity is a measure of calcium, magnesium, and other acid-moderating compounds that act as a buffer to pH change. What is important to understand about alkalinity is that it helps stabilize the pH balance, preventing sudden pH changes in your water, thus keeping the pH within a normal range. There is often some confusion about pH and alkalinity when it comes to water chemistry, the misconception is that these are the same thing.
When you measure pH, you are checking how acidic or alkaline the water is. The range goes from 1 (very acidic) to 14 (very alkaline), with 7.4-7.6 being neutral and a place where Chlorine works at its best. Alkalinity (or total alkalinity), on the other hand, is not measured like pH on a scale but in parts per million (ppm) of those compounds mention prior. The recommended range for a pool or hot tub water alkalinity should be between 80 and 120 parts per million. Any good water testing kit can help you determine the range, or you can take a sample of water to your local pool or hot tub store.
If your Alkalinity is Below 80 parts per million (ppm) alkalinity will result in your water being too Acidic, this can cause:
Corrosion of surfaces and equipment
Etching and staining of surfaces and equipment
Burning or itching of the eyes and skin
Water may turn a shade of green
Wild fluctuations in pH levels
If your Alkalinity is Above 120 parts per million (ppm) alkalinity will result in your water being too alkaline, this can cause:
Scaling of surfaces and equipment
Burning or itching of the eyes and skin
Water may turn cloudy
A high pH level that’s more difficult to lower
There are many reasons why alkalinity will go up or down in your pool or hot tub water. It can be from natural environmental or bodily causes, as well as everyday treatment chemicals. Keeping Alkalinity in the range not only makes your swimming or soaking experience more enjoyable, but is very important to the life of the pool or hot tub and its components. Adjusting the Alkalinity is something that should be done incrementally. In other words, it is better to make slight adjustments when the Alkalinity gets a high or low than to wait for the Alkalinity to get way off and try to adjust it all at once, which can make the processes more difficult. If the Alkalinity is way off, I recommend adjusting and then retesting after 24 hours and adjusting again if necessary.
What Causes Alkalinity to Rise
If your pH level goes up, this will begin to increase your alkalinity along with it. An increase in pH typically comes from body lotions or sweat washing off into the pool or hot tub. You could also be using a high alkalinity water source. It’s also not uncommon for owners to go a bit overboard when shocking their water, and since the chlorine-based shock is high in alkaline ingredients that will naturally raise your alkalinity.
To lower the Alkalinity level, you can use Muriatic Acid (liquid) or Sodium Bisulfate (granular). Both can also be used to adjust pH it is just applied differently. I would only recommend Muriatic Acid for Swimming pools, as Muriatic acid is extremely caustic. It can burn your skin, and the vapor from muriatic acid can cause respiratory problems. Be sure to read the directions or consult the store you purchased it from for proper use and precautions. Most pool stores recommend this for high alkalinity because of its low cost compared to Sodium Bisulfate, and a lot of liquid acids can go a long way in a large pool. That being said, both can be used to significantly lower your alkalinity while keeping your pH as stable as possible. The directions for both types of acid are the same, start with shutting off your pump before adding the acid. When the pump is running, it circulates the acid, but it also adds oxygen through churning and causing the water to bubble. The oxygen then amplifies the effects of the acid on the pH, which is fine if you are trying to lower both pH and alkalinity.
What causes Alkalinity to Fall
If your pH level is on its way down, it will eventually begin to decrease your alkalinity. A decrease in pH can be caused by sweat or excessive rainwater entering a pool and diluting it, acid rain can directly drive both your pH and alkalinity levels down. Shock can raise pH, as explained above, but a common chlorine tablet has the opposite effect. When dissolving into your pool water, it will lower your pH level and alkalinity along with it. To raise the Alkalinity level, you would add Baking Soda (Sodium Bicarbonate). Baking Soda can raise the pH of the water slightly because again both Alkalinity and pH are tied together. This also makes it perfect for hot tubs, as they typically need only small Alkalinity adjustments. So, in turn, it will also fix low pH at the same time. If both the pH and Alkalinity are low use, Soda Ash, until the pH comes to the proper level, then use Baking Soda to make further adjustments to the Alkalinity if needed. NOTE: Soda Ash (Sodium Carbonate) and Baking Soda (Sodium Bicarbonate) are NOT the same things. Soda Ash is used for adjusting pH and Alkalinity, Baking Soda is primarily for adjusting Alkalinity.
I hope this has been helpful as I am knowledgeable on this subject but would not call myself an expert. In writing this article as I wanted to be as accurate as possible without making it complicated, so I did get a little help from some online resources.
Keep on Swimming N Soaking!
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