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Pool Owner’s Guide · Your Water
Calcium Hardness: Gentle on Plaster, Kind to Tile
by Spectrum Pool Care
Every pool holds a little dissolved calcium, and the right amount keeps plaster smooth and tile clean. Here’s what calcium hardness is, and how it fits with the rest of your water.
Calcium hardness is the amount of dissolved calcium in the water, the same mineral that gives “hard water” its name. Water naturally seeks a balance with the surfaces around it. If it holds too little calcium, it slowly draws some from plaster and grout. If it holds too much, it sets the extra down as scale.
For plaster and other cement-based pools, the target is 200 – 400 ppm. Vinyl and fiberglass pools usually do well a little lower, around 150 – 250 ppm.
Finding the Balance
Too Soft, Just Right, Too Hard
Too soft
Water that’s low in calcium pulls calcium from plaster, which over time can leave surfaces rough or etched.
Just right
Plaster stays smooth, tile stays clean, and the water neither takes from surfaces nor leaves deposits.
Too hard
Extra calcium can settle as white scale on tile, inside heaters and on salt cells, and can make water look dull.
Working together
Calcium, pH, alkalinity and temperature act as a team. Warm water with high pH is when scale forms most readily.
Close to Home
Hard Water and the Valley Sun
Tap water across much of the San Fernando Valley and the Westside arrives with a fair amount of calcium already in it. Then the sun takes over. As water evaporates on hot days, the calcium stays behind, so every top-off adds a little more. Over a few years, calcium hardness in many local pools climbs slowly upward.
Raising it is simple: calcium chloride, added gradually.
Lowering it takes fresh water. Calcium isn’t used up, so replacing part of the pool’s water is the practical way to bring it down.
Keeping pH and alkalinity in range helps calcium stay dissolved, even when hardness runs toward the upper end.
From our routes: we keep pH and alkalinity balanced so the calcium in local water stays where it belongs, in the water. If we notice scale starting to form at the tile line, we’ll let you know.
