How to lower alkalinity in your pool
Most pool owners are aware of the importance of chlorine in keeping a pool sanitized, safe, and free from green tints. But there are many other pool chemicals that go into making a pool inviting.
Bases and acids are among the most important, next to your basic detergents like chlorine and bromine. These chemicals raise and lower your pool’s overall pH and alkalinity, affecting the balance of the water, and the effectiveness of the detergent.
If your pool’s alkalinity is too low or too high, your pool pH levels may fluctuate rapidly, leading to issues like burning eyes and corrosion, or cloudy pool water.
What is alkalinity?
Alkalinity is a measure of the alkaline substances in your pool – usually sodium carbonate or bicarbonate. Total alkalinity needs to be in harmony with your pool’s overall pH.
As a basic reintroduction to chemistry, the pH scale runs from 0 to 14 (for most substances, with a few exceptions outside the scale) with 0 being most acidic, and 14 being most basic. pH itself is a measure of the concentration of positive hydrogen ions in a solution – the closer to 0 a substance is, the higher the concentration.
Pool water should have a pH of about 7.4 (relatively close to neutral), and a total alkalinity of 100 to 150 parts per million (ppm). Different tests are used to measure these values, and they’re readily available online.
Lowering the alkalinity in your pool
High pool alkalinity (and a high pH) cause cloudiness, clogged filters, calcium scaling, and can damage your pool’s circulation. Your detergent will need to work harder to keep the pool clean, which means you need more chlorine, which means you need to pay for more chlorine. Generally speaking, it’s much cheaper to lower your pool’s overall alkalinity (and pH) than to compensate with more chlorine and a clogged filter.
Thankfully, all you need to lower your pool’s alkalinity is an acid. Common acids used in pools include sulfuric acid and muriatic acid.
Sulfuric acid is the more severe and dangerous of the two. Muriatic acid is also commonly used. You can also use a pH decreaser like sodium bisulfate, which is a slightly neutralized form of sulfuric acid (after it’s been combined with a basic sodium base).
The exact values for how much acid you will want to use depend on your pool’s overall size, and the reading on your test strips. There are multiple online calculators to help you figure out the ideal volume of acid, as well as which acid to use. Note that your acid’s manufacturer matters as well. Different manufacturers use different concentrations. Your chosen acid should come with instructions on how much to use.
Be sure to handle any acid or pH decreaser with great care, and do not use your pool for at least six hours or more after using the acid. Please handle acid only with gloves, goggles, and a mask.
What about raising alkalinity?
Okay, so maybe you’ve gone a little overboard with the acid – or, you just want to know what you should do if your alkalinity has dropped too low. Thankfully, you can raise the alkalinity of your pool with a relatively common chemical: baking soda.
Yes, the same baking soda you might use to clean or bake with. You don’t need a fancy pool equivalent – any baking soda will do the trick. Just keep in mind that you would need quite a bit of it. One and a half pounds of baking soda is needed to raise the alkalinity of a 10,000-gallon pool by about 10 parts per million.
You may have also heard people recommend soda ash to get the job done. Soda ash is sodium carbonate, where baking soda is sodium bicarbonate. The chemical and molecular difference between the two is best described like this: where soda ash slightly raises alkalinity and greatly raises pH, baking soda will greatly raise alkalinity and slightly raise pH.
This is because soda ash has a much higher pH than baking soda (it is more basic), thus affecting a pool’s pH level to a greater degree. While you can play around with your pool’s chemical composition a little bit using soda and acid, too much experimenting will require you to dump some of your pool water and bring in fresh H2O, due to an excessive number of particles in the water.
If you aren’t sure what to add to your pool, and how much, your best bet is to take a few samples of your pool’s water and visit a local pool expert. They will be able to advise you on how to treat your pool to get its balance right – and they’ll probably even stock everything you need to do the job right away.
Understanding pool water balance
Alkalinity and pH levels are two of multiple different metrics used to rate a pool’s overall water balance, which serves to keep a pool clear, free from bacteria, and safe to swim in while increasing the longevity of your pool’s plaster and avoiding calcium scaling on the walls of your pool.
Pool water balance is a very fickle thing, and the equilibrium of a pool’s chemical state is exceptionally fragile. Sunlight, for example, removes most of the free chlorine in a pool, which is why you need to check chlorine levels most often. Other relevant levels include your metal levels (treated with a metal sequestrant), calcium hardness, and cyanuric acid (used to protect chlorine from UV rays).
These levels exist in harmony with each other. Chlorine effectiveness is limited in a pool with too high or too low pH. Alkalinity and pH are intrinsically linked, as alkalinity is raised or lowered using bases and acids (just like pH).
Calcium hardness is based on the total levels of calcium and magnesium in your pool and is generally treated by adding either (or both) if your calcium levels are too low, or by draining your pool a bit to introduce fresh water, or using a calcium sequestrant if your calcium levels are too high.
Be sure to check your levels
Pool experts will give you differing opinions on how often you should check your water balance, but most would agree that you will want to perform different checks at different intervals.
Chlorine, for example, is best measured at least twice a week. Calcium hardness, on the other hand, remains stable for a relatively long time – it’s perfectly fine to check it once a month. Alkalinity should be checked at least about once a week, and you should check your pH levels with your chlorine.
Weekly pool maintenance will save you thousands of dollars in the long run, by preserving the longevity of your pool equipment and plaster while reducing the risk of algae blooms and other intensive clean up operations. It’s also the key to keeping your pool pleasant to swim in.
A few minutes of skimming every day, the occasional pump filter check, and keeping an eye on your chemical levels is often all it takes to keep your water clear and safe.