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    Pool Water Chemistry

    In swimming pools, there are four components of pool water balance; your pool water pH, Alkalinity, Hardness and Cyanuric Acid levels. Test your water regularly and adjust as needed, to keep water balance within the proper ranges. Balanced pool water helps your chlorine be more effective, and also protects your pool and pool equipment from stains, scale and corrosion.

    Pool water is considered "balanced" when pH, Alkalinity, Calcium Hardness and Cyanuric Acid levels are all within their proper ranges:

    • pH: 7.2 to 7.8
    • Total Alkalinity: 80-120 ppm
    • Calcium Hardness: 180-220 ppm
    • Cyanuric Acid: 30-50 ppm

    However, within these ranges, there are ideal levels which work best; each component of water balance affects the others, and water temperature also plays a large role in the most ideal water balance levels.

    80 years ago, chemist Wilfred Langelier developed the Langelier Saturation Index, to determine the saturation point of calcium under a matrix of water balance measurements. It's a complicated sequence of calculations, but nowadays, you can use an LSI Calculator. Just type in your pH, Alkalinity, Calcium Hardness, Cyanuric Acid levels, and your water temperature, to see your pool water's propensity to scale or corrode.

    Although there are several online, the Pentair LSI calculator is the most user friendly. After entering your numbers, click Calculate to produce a numerical result, or your LSI. A result between -0.3 and +0.3 is considered balanced. LSI results lower than -0.3 indicate aggressive and corrosive water conditions, which can damage soft and shiny surfaces. LSI results higher than +0.3 indicate scaling water conditions, which can deposit on pool surfaces, or create frequent cloudy water.

    Pools with high calcium hardness or low alkalinity, for instance - can still be "in balance," depending on your levels of pH, Cyanuric Acid and water temperature. For truly balanced pool water, test all 4 components of water balance, and the water temperature, and run an LSI test.

    To check your own pool water balance, you need a full-featured test strip or test kit that will check all 4 water balance components, plus Free and Total chlorine levels. 7-way test strips by AquaChek or 6-way Insta-Test strips both perform the full battery of tests, as well as your more full featured test kits, like the Taylor K-2005 or the ColorQ Pro 7 test kits.


    Pool pH

    pool ph chemicalsYour pool pH should be in the range of 7.2 to 7.8. Although the range of 0.6 tenths may seem small, pH is a logarithmic scale, which means that each 0.1 movement is actually 10 times more acidic, or more basic, than adjacent numbers.

    The best pool pH level is usually on the low side, 7.2-7.4, so that your chlorine works more effectively, however, for proper water balance, your Ideal pH level depends on other water balance components, and can be determined by calculating your Saturation Index, as described above.

    Pool pH levels are dependent on pool Total Alkalinity levels, which should be 80-120 ppm. Low alkalinity levels cause "pH Bounce," and make it hard to maintain a stable pH level. High alkalinity levels cause "pH Lock," and make it hard to adjust pH levels, either higher or lower.

    What causes High pH in pools

    • Low Total Alkalinity level
    • New Pool Plaster
    • Aeration from water features
    • Aeration from salt water chlorine generators
    • Use of high pH chlorine (Sodium Hypo or Calcium Hypo)
    • High pH fill water (from the hose)
    • Overdose of pH increaser
    • Algae in water, absorbing Carbon Dioxide

    What causes Low pH in pools

    • Heavy rain water, average pH of 5.6
    • Low pH of chlorine tablets, pH of 3.0
    • Heavy leaf, lawn or planter debris
    • Bather waste; sweat, body oil, urine
    • Heavy wind-blown dust or pollen
    • Overdose of pH decreaser
    • Low pH fill water (from the hose)

    How to Lower Pool pH

    • Turn on pump to circulate water
    • Test Total Alkalinity, adjust to the 80-120 ppm range
    • Add 4 oz of Liquid Acid or Dry Acid, per 10000 gals, to lower pH by 0.1
    • Pour along the edge of the pool to distribute pH decreaser chemical
    • Test pool water again after several hours

    How to Raise Pool pH

    • Turn on pump to circulate water
    • Test Total Alkalinity, adjust to the 80-120 ppm range
    • Add 4 oz. of Soda Ash, per 10000 gals, to raise pool pH by 0.1
    • Sprinkle along the pool edge to distribute pH increaser chemical
    • Test pool water again after several hours

    Pool Total Alkalinity

    pool alkalinity increaserYour pool Alkalinity level should be 80-120 ppm. Alkalinity is a measurement of the carbonates and bicarbonates dissolved in your water, and it serves as a pH buffer. Lower alkalinity levels in the pool may not buffer pool pH levels enough, and pH levels can be erratic. Conversely, high alkalinity levels provide too much buffer, making it hard to adjust pH levels in the pool. High alkalinity levels can also contribute to cloudy or hazy pool water, and to scale formation, when conditions are right.

    The causes of high total alkalinity in pools is the same as the reasons for high pH in a pool. High alkalinity can also be caused by an over dosing of sodium bicarb for pools, or Total Alkalinity Increaser.

    Likewise, the causes of Low Alkalinity tend to be the same things that cause low pH - the use of low pH chlorine tablets, acidic rainfall, acidic plant debris, and bather waste.

    How to Lower Alkalinity in Pools

    • Turn off pump and allow water to become still
    • Add pH Decreaser in one corner of the deep end to lower pH to 7.0-7.2
    • Raise pH to 7.2-7.4, and re-test Total Alkalinity
    • Repeat if Alkalinity remains too high

    You can't reduce total alkalinity levels without also pummeling your pH level, because the same chemical (Liquid Acid or Dry Acid) is used to lower both pH and Alkalinity in pools. Pooling your pH decreaser in one calm and still area of the pool (or in an attached spa) increases hydrocarbon exchange resulting in a greater reduction in Alkalinity levels, as opposed to walking your pH decreaser, or pouring it around the edge of the pool.

    How to Increase Alkalinity in Pools

    • Turn on pump to circulate water
    • Sprinkle Alkalinity Increaser along the pool edge to distribute
    • Test pH and Alkalinity again after several hours

    How much alkalinity increaser to add to your pool depends on your pool size and current tested level of total alkalinity; adding 1.25 lb. of Total Alkalinity Increaser, per 10,000 gals, will raise pool alkalinity by approximately 10 ppm.

    Your test for total alkalinity should be in the range of 80-120 ppm, after making adjustments with a pool alkalinity increaser. Since bicarb is also a base, adding alkalinity increaser will also raise pH slightly. If your pH level is now too high, walk an acid (liquid or dry) around the pool edge to lower the pH back into range.


    Pool Calcium Hardness

    pool hardness increaserPool calcium hardness levels should be 180-220 ppm, although pools can operate effectively at 400 ppm or higher. Vinyl pools can handle lower hardness levels, or softer water in the 150 ppm range, because there is no calcium based plaster or grout surfaces. However, very low hardness levels can corrode metals. Pool ladders, pool lights, copper heaters, sensors and other stainless steel parts can corrode in very soft water, due to low levels of calcium or magnesium cations.

    Very high levels of hard water, common in many parts of the U.S., can also create problems with scaling, staining and cloudy water, in addition to interfering with sanitation. Pool water that is too soft can become aggressive in a hunger for calcium and can begin to leach it from tile grout and pool plaster. Low calcium hardness levels also make it easier for a pool or spa to begin surface foaming, and corrosion of soft and shiny pool surfaces can result.

    How to Lower Hardness in Pools

    Lowering calcium hardness levels can be particularly tricky, and the easiest way is to drain a portion of the pool and refill with softer water, perhaps delivered by truck, if your tap water is also hard. There are some other methods to lower calcium hardness listed below, which are more involved and more expensive to undertake.

    • Drain a portion of the pool and refill with softer water
    • Raise pH to precipitate Calcium, then use Floc to sink particles to floor
    • Try Cal-Treat by United Chemicals
    • Water softening with truck mounted reverse osmosis filters

    How to Raise Calcium Hardness in Pools

    Increasing calcium hardness levels in pools is much easier than lowering the level. Just add Calcium Hardness increaser to raise pool hardness. Calcium Hardness levels are slow to change, and typically only one or two increases to hardness levels is needed during the pool season.

    How much calcium hardness to add to your pool depends on your pool size and current tested level of water hardness, but adding 1 lb. of Calcium Hardness Increaser, per 10,000 gals, will raise pool hardness by approximately 10 ppm.

    • Turn on pump to circulate water
    • Fill a clean 5 gal. bucket with water
    • Add 1 lb Calcium Hardness Increaser, per 10,000 gals, to raise level 10 ppm
    • Stir to dissolve (solution will become warm)
    • Pour Hardness Increaser around edge of pool
    • Test Calcium Hardness level again after several hours

    Pool Cyanuric Acid

    pool stabilizerPool Stabilizer is made of cyanuric acid, and levels should be 30-50 ppm. Cyanuric Acid is often labeled as pool conditioner or pool stabilizer, and bonds with free chlorine molecules to shield them from UV degradation by the sun. Although technically a part of the Langelier Saturation Index, it actually has only a small influence on the other components of water balance. For outdoor pools however, cyanuric acid is necessary to prevent the loss of chlorine during sunny parts of the day.

    Why Use Pool Stabilizer?

    Pool stabilizer should be tested for several times per season and kept within range. If your Cyanuric level is too low, you will use much more chlorine to maintain 1-2 ppm of Free Chlorine, and may be unable to maintain it during the hottest parts of the swim season. Cyanuric acid or pool stabilizer has the effect of suppressing the activity of the chlorine molecule, which means that the killing power is also affected. The higher the level of cyanuric acid is, the less active your chlorine becomes. At pool stabilizer levels over 100 ppm, the suppression is so strong that you may be unable to obtain a chlorine reading.

    Trichlor tablets and Dichlor shock are two forms of stabilized chlorine, which contains small amounts of stabilizer. For a fresh pool fill, you will want to add stabilizer to raise the level to 30 ppm, at which point the small amounts added to your chlorine tablets will replace any lost to backwashing and splash out.

    How Much Pool Stabilizer to Use

    1 pound of granular stabilizer, per 10,000 gals., will raise cyanuric acid levels by about 10 ppm. For a 20,000 gallon pool, freshly filled with water containing no stabilizer (which is normal), use 6 lbs of cyanuric acid to reach 30 ppm, or 10 lbs to reach 50 ppm. If you use the liquid stabilizer, our Instant Pool Conditioner, the dose is 1 gallon per 10,000 gals. of pool water, will add 35 ppm of stabilizer.

    How to Test for Pool Stabilizer

    The test for cyanuric acid is performed several times each season to be sure the level of pool stabilizer is not too high or too low. The test is not included in more basic test kits or test strips, but is included in 6-way and 7-way test strips, or full featured pool water test kits.

    Test strips use the standard color comparison method for testing pool stabilizer, but stabilizer test kits like the Taylor K-1720 use a turbidity test, where CYA reagent is mixed with pool water, 50/50. The solution turns cloudy in the presence of CYA. Fill the test vial with the cloudy mixture, just until the black dot on the bottom becomes invisible. Check the stabilizer level on the side of the test vial for the cyanuric acid reading, in ppm.

    How to Apply Pool Stabilizer

    • Pour stabilizer into a 5 gal. bucket filled with clean water, dissolve and pour around the pool.
    • For sand filters, you can slowly pour the stabilizer into the skimmer with the pump running.
    • For plaster pools, you can broadcast stabilizer across the surface, and brush to distribute.

    How to Lower Pool Stabilizer

    • Drain and refill a portion of the pool with unstabilized fresh water.
    • Apply BioActive to remove cyanuric acid from pool water.