Swimming Pool Blog

Lowering Pool Calcium Hardness Levels

Lowering Pool Calcium Hardness Levels
Mark Garcia July 25, 2015

Total water hardness - it's a measure of all the mineral salts in a pool, calcium, magnesium and even sodium, by mostly calcium. The amount of calcium in your water is an important component of overall water balance. Too little calcium and soft water becomes aggressive, attacking cementitious surfaces. Too much calcium, and hard water can produce stains and scale, and cloudy water. It can also interfere with sanitation.

So, too much calcium hardness is a bad thing. How much is too much? Normal range for swimming pools is 180-220 ppm, although some people say 200-400 ppm. Anything north of 500 ppm would be considered very high, but there are pools that can run higher than that without problems. However, for many pool owners and operators in hard water areas, the question is often asked: 


How Do You Lower Calcium Hardness Levels in a Swimming Pool? 

Several things can contribute to high calcium hardness levels in a pool, such as a heavy reliance on calcium based pool shock, calcium hypochlorite, or an indoor pool that gets very little dilution - but for most people, it's already high to begin with. In many areas of the country, water is hard right out of the tap, even after treatment with a water softening and filtering system. For those of you with hard water, and you know who you are - this blog post is for you.

Reverse Osmosis Filtration

 Due to the water crisis and drought conditions in many parts of the south and west, many pool owners (and spa owners) are prohibited from draining the pool. This rules out the Dilution Method (see below) for lowering calcium hardness. Innovative entrepreneurs have answered the call by operating mobile pool filtration units. Using huge truck mounted reverse osmosis filters and water softening agents and pH control, they can pump your entire pool through the truck a few times and return to you fresh and balanced pool water, with calcium hardness removed to an appropriate level.

Precipitate and Floc

There are still some old pool guys that insist on this method, but it can be risky. The idea is to carefully raise the pH with sodium carbonate or soda ash, to a point above 8.2, or off the scale. When conditions are right (meaning temperature), the excess calcium in the water will begin to precipitate and visibly cloud the pool, turning it milky white. Then, using a flocculent like Aluminum Sulfate or PhosFloc, you drop all of the suspended particles to the floor, and vacuum it out to waste. Then lower the pH level back to around 7.4, and check your Alkalinity. Calcium Hardness can be lowered by dramatic amounts with this method, but you risk staining or calcium deposits on pool surfaces.

Cal Treat

Cal Treat is a product produced by United Chemical. It uses a form of Dry Acid to remove light scaling and reduce calcium hardness levels without draining, according to the manufacturer. Use one bottle per 15,000 gallons, to reduce calcium hardness below 400 ppm. Actual ingredients for the formula are a closely guarded secret, but some claim that it may have a form of phosphates. Reviews are mixed, for some people it seems to work well, and for others, the results were less than expected. Your mileage may vary.

Drain & Refill

The oldest method for reducing calcium hardness in a pool, drain out a portion of the water (or all of the water) and refill the pool with softer water. Easy - except when you can't drain your pool, or your fill water is even harder than your pool water. In situations like this, you can order water delivery, by truck. It's an expensive option, with 5000 gallons going for $250 in most places. But, sometimes a tough situation demands a tough solution, maybe just a few truckloads of water? 

Zeolite Filter Sand

If you have a sand filter, you can replace regular pool filter sand with ZeoLite pool filter sand, which has the ability to trap the very tiny particles of calcium carbonate. It does this not by filtering out the particles, but by ion exchange. Calcium and magnesium ions are exchanged for sodium ions in the zeolite sand bed, with softens the water. The trapped calcium hardness is then simply backwashed out of the pool filter. Zeolite filter sand needs to have the ions refreshed after a few years, flushing it with a strong sodium solution, a Zeo Filter cleaner will restore it's ionic charge.

Poolside Water Softening

Home water softening units can be setup next to the pool, and using a small pool pump or submersible pump, you can pump the pool water through the water softening filters (which use sodium and ion exchange to lower calcium levels). After the water is pumped thru the water softener, a discharge hose pumps it back into the pool. A system large enough to handle a pool might set you back $500 or so. If your home already has a water softening unit, often times the outdoor spigots are not connected to the system, but the Utility sink or Laundry room sink may be a better way to fill or refill the pool. 


Thanks for Reading!
Mark Garcia