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    Pool Scale: Remove & Control

    May 8, 2019
    Sheryl Somers

    calcium scale on pool tiles, image credit to chemistryland.com

    When we talk about Pool Scale, we are predominantly concerned with calcium scale, which shows up as thin layers or as nodules and crusty deposits on pool surfaces.

    Pool scale can be unsightly, and mostly because the relatively translucent calcium mixes with other darker colored contaminants. Calcium scale is positively charged, it naturally attracts negatively charged particles, on its way to depositing as a film or crystal.

    Pool scale may be more of a problem in certain 'hard-water' areas of the country, where water comes out of the tap at a level of hardness that makes drinking glasses spotty, skin super-squeaky, and soap scum difficult to remove.

    Hard water also makes it more likely that scale deposits will form on your pool, causing surface staining or scratchy crystalline bumps on plaster or crusty layers on the tile or at the waterline.


    • High Calcium Hardness levels
    • High Total Alkalinity levels
    • High pH levels
    • Warm water temperatures

    The primary cause of pool scale deposits at the waterline or on underwater surfaces is the pool water chemistry. When high levels of calcium and carbonates combine to form calcium carbonate, conditions can cause it to deposit. High pH levels and warmer waters make molecules more active, making scale stains more prevalent.

    The best way to control for the various elements leading to pool scaling is to perform a regular test known as the Langelier Saturation Index, or LSI for short. An LSI test determines a pool's preponderance for scaling or etching. A pool is considered to have a balanced LSI when results are -0.3 to +0.3. Test results below -0.3 indicate a prevalence toward corrosion - and above +0.3 and your water is 'scale-forming'.

    The math is a bit complicated to calculate the LSI, but you can use the Pentair LSI Tool - just plug in your water test levels and it crunches the numbers for you! The tool is then used to see the effect of adjusting chemical levels.


    Efflorescence is also a form of pool scale, but it comes not from your pool water, but from moisture contained within raised rock walls, or beneath the pool coping stone. It can be seen coming out of mortar joints between stones on a raised rock wall, or can drip down onto pool perimeter tile, flowing from the mortar bed beneath pool coping stones.

    Efflorescence can be slowed by using Clear Sealer on rock or brick faces, and making sure that pool caulking is maintained to keep water out of the expansion joint. For raised rock walls, applying a bitumen or similar waterproofing on the backside of the wall can be used to block the moisture seeping through the wall.


    - POOL TILE SCALE: If tile scale deposits are heavy, make the first pass with a flat scraper like a 1" putty knife.

    • Acid Magic and scraping
    • Bead blasting or sand blasting
    • Flap wheel, nylon wheel or bristle disk on a cordless drill

    - POOL SURFACE CRYSTALS: Nodules are usually quick to remove with the right technique and equipment.

    • Acid Magic and scraping
    • Belt Sander or Sanding Blocks
    • Pressure Washing with water

      • calcium nodules, image credit to poolcenter.com

        - CALCIUM FILMS: Sheets of calcium carbonate often go unnoticed on white plaster pools, until layers thick.

        • Acid Magic or No-Drain Acid Wash
        • Double-dose of Metal Klear or Scale Free
        • Jack's Magic The Copper & Scale Stuff


            Once you remove pool scale, how do you prevent it from coming back?

            • Maintaining water balance to avoid over-saturation, using the LSI calculator
            • Regular use of Scale Free, Stain Away or other high quality sequestering agent
            • Use a fill-water filter like the Pleatco Pre-Filter, when topping off the pool
            • Brush your pool regularly with a good pool brush in good condition.

            • Natural Chemistry Scale FreeSequestering agents will keep calcium and carbonates safely locked in solution, where they cannot precipitate [out of solution] to cause problems. Important to note that sanitizers and sun deplete sequestering agents, so they must be added every week or two, to maintain protection.

              Scale Free is particularly formulated for control of calcium carbonate in pools, used for effective control of pool scale.


    Blog Author
    Sheryl Somers
    SPP Pool Expert