What Chemicals are Needed to Open a Pool?

The time to think about maintaining a pool or hot tub is during the winter, including consideration about what chemicals are needed to open a pool once the warm weather returns. Whether you’re responsible for a private or public swimming pool, understanding how these chemicals interact with pool water will help ensure that the water will be clean and safe for swimming. Oh, and for those fortunate to have access to an indoor pool or hot tub, this information may be useful for you right now!

Testing the Water

Before looking at what chemicals are needed to open a pool, however, it’s a good idea to test the water to see what chemicals it might need. Imbalanced pool chemistry can cause all sorts of problems for both the pool’s infrastructure and those who use it. Testing can be done with either test strips for a quick result or a liquid test kit, which tends to provide more comprehensive results. For the most accurate results, take a water sample to a trusted pool supply company.

Temperature makes a difference, as chlorine dissipates more quickly above about 80 degrees Fahrenheit, causing calcium carbonate deposits to form. Additionally, algae blooms and bacterial growth occur when chlorine levels are too low. Pool liners and other equipment can erode because of an imbalance in pH levels. Low alkalinity can also affect pH levels, causing overly acidic water that can erode your pool.

The following are recommended test levels (ppm = parts per million):

  • Alkalinity: 80-120 ppm
    pH levels: 7.2-8.0 (though the ideal is between 7.4-7.6)
  • Cyanuric acid: 20-50 ppm
  • Chlorine: 1-2.5 ppm (minimum 1.0 of free chlorine residual level; 1.5-2.5 ppm with un-stabilized chlorine; 2.0-2.5 with stabilized chlorine)

The best place to take a sample is from water at the pool’s center and away from skimmer openings or return jets, using a clean container. Care must also be taken when adding chemicals to ensure the pool isn’t overloaded with them or that there’s no unforeseen interaction between different chemicals. Along with testing for the above, swimming pools and hot tubs should be tested weekly for calcium levels, which should fall between 200-400 ppm for pools and 150-250 ppm for hot tubs.

Applying the Chemistry

After testing, the chemistry is fairly straightforward. The test essentially tells you what chemicals are needed. To open a pool and make the water safe for swimming, make sure to pay attention to the following water quality issues.

Alkalinity & pH Levels

Generally, testing your pool water’s alkalinity should be addressed first, with pH levels dealt with next. Alkaline substances are present in all water, and the higher the alkalinity the more it inhibits changes in pH levels. Testing will determine whether it’s too high, too low or just right. If your pool’s initial test shows alkalinity outside the recommended range, then you will need to add chemicals.
When calcium scaling or pH levels rise significantly, alkalinity will require lowering. Use a strong acid to lower pH levels, such as muriatic acid or sodium bisulfate.

To increase total alkalinity, add sodium bicarbonate, more commonly known as baking soda. Generally, it takes 1.4lbs to increase alkalinity by 10ppm in 10k gal of water. Add this in increments until the water reaches an acceptable level.

It’s important to also remember that pH is a measure of the acidity – as opposed to the alkalinity – of the water. The lower the pH, the more acidic the water is; when pH goes below 7.0 swimmers will experience irritation to eyes and mucous membranes. Low pH also damages plaster finishing and corrodes metal piping. It’s also advisable when introducing acid to pool water to dilute it in a bucket of water so as not to stain pool walls.

Adjusting Calcium Levels

Calcium levels are interlinked with pH, temperature and disinfectant levels. Though typically not a major concern for maintaining pools, calcium levels should still be checked regularly, and the best time to address this is when opening a pool for the season. If levels are too high, calcium deposits can obstruct filters and piping. When calcium levels are too low, it can erode a pool’s walls.

While lower calcium levels aren’t generally a problem, water that’s too soft will corrode your pool, dissolving concrete and plastic while increasing corrosion on any submerged metal parts. In such cases, using calcium chloride will raise levels and decrease acidity.

Though too much calcium in your pool water doesn’t cause immediate issues, it results in buildups that can result in having to repair or replace clogged pipes and filters. Higher calcium levels are often the result of minerals occurring naturally in the water, and as such corresponds with higher alkalinity levels. In some cases, just adding freshwater can help lower calcium levels, though this won’t work if the water being added is calcium-rich. Muriatic acid will help lower calcium hardness, though you may have to go back and readjust alkalinity.

Typically, for pools with fiberglass or vinyl linings, calcium hardness should be between 175-225 ppm. For concrete or plaster pools, levels should range from 200-275 ppm.

Cyanuric Acid Levels

A common chemical for preventing chlorine loss, cyanuric acid protects free chlorine – the chlorine that’s not yet mixed with the pool’s water – from the sun’s ultraviolet rays. It stabilizes chlorine levels and helps maintain proper sanitation while keeping down costs by reducing the amount of chlorine you need to add.

Essentially, cyanuric acid builds up over time and is often a stabilizer in chlorine that you add to your pool. As such, it may not need to be added as frequently throughout the season, though it’s one that will save money by reducing the amount of chlorine you need to add throughout the swimming season.

When there’s too much cyanuric acid in a pool, however, bad things can happen, such as:

  • Reducing disinfectant properties of chlorine
  • Slowing chlorine’s ability to kill microorganisms and prevent algae
  • Increasing cloudiness

The only way to reduce cyanuric acid involves replacing pool water with fresh water.

Contact the Halogen Pool Supply Experts

Halogen Pool Supply supplies residential and commercial clientele throughout the United States and Canada with a variety of chemicals necessary for keeping water in swimming pools and spas safe, along with a variety of other pool supplies and equipment. With over 80 years in the business, the company’s knowledgeable team can provide advice on what chemicals are needed to open a pool, along with the best products to use for keeping the water clean and safe. Contact Halogen Pool Supply for all your pool product needs.