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Thread: Scale and the CSI vs LSI

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    Scale and the CSI vs LSI

    I lowered my water line by an inch and now I see a new scale line.

    I have recently been enlightened, having learned about TFP, water balance, CSI, etc. Before my enlightenment, I had allowed a stark ring of scale to form. Most likely by allowing my CSI to drift too high in the positive range. At the beginning of the summer I removed this scale with elbow grease by chipping and scrubbing with pumice stones.

    I am now a little discouraged because the scale is beginning to return. I have tested my water almost daily throughout the summer and have kept my CSI in the negative range -0.1 to -0.3.

    The CSI is an overall indicator of corrosive versus scale-prone water. Water with a CSI level that is slightly negative should remove just a tiny bit of scale - not deposit it.

    For example:

    FC 4.6
    CC 0.2
    pH 7.5
    TA 50
    CH 550 (fill water 110)
    CYA 40
    Salt 3800-4500 (depending on who does the test)
    Temp 88
    CSI -0.27
    LSI 0.13 (from the Taylor Watergram wheel)

    My CH is high so I have to be careful to keep the CSI out of the positive range. However, the corresponding LSI is slightly positive. I hate to say this but does this mean that the LSI is more accurate? If it were more accurate it would explain the deposit of the scale. Am I correct in assuming that slightly corrosive water should not deposit scale?

    I may need to do a partial drain to get the CH down so that I don't have to fight the scale as hard.
    Arizona. 22K Gal, IG, rectangular, plaster. SWCG IntelliChlor IC40. Pentair WhisperFlo 1.5 HP 2 speed
    Pentair Clean & Clear Plus 420 sq ft cartridge filters. in-floor. Pool completed April, 2008. K-2006.

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    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Scale and the CSI vs LSI

    Scale can deposit on the water line even with a somewhat negative saturation index due to evaporation of the water which concentrates calcium carbonate (you can get salt deposits this way as well). That is, as the water evaporates it can deposit solids on the surface. If the saturation index were too high, you would be getting scale in submerged areas as well. You want the saturation index set to protect your overall pool surfaces. Weekly brushing will usually be enough to prevent a scale line -- when I brush my pool I include the tile line during the brushing. If that isn't enough, then someone else may suggest a product that might help.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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