water softeners on a pools

Total hardness and calcium hardness in pool water.
Scale, calcium buildup, hard water and scaling problems.
aquila

water softeners on a pools

Postby aquila » Thu 24 Jan, 2008 18:53

I am by no means a chemist, but need an answer to a simple question. On a non salt-generator pool, is soft water desirable or not? My dad has had a pool company for 18 years. I've worked it for 6 years and everybody I have talked to in the industry has spoke against soft water in pools. The reason being, simply that the chemicals require a certain amount of hardness to work.
Is this true or not? I have a customer that recently had soft water hooked up to his house and in doing so, had it hooked up to the pool. Now he is wondering if he will have problems. What do you think?
Thanks,
Tom in Tucson


chem geek
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Postby chem geek » Thu 24 Jan, 2008 19:10

It depends on the type of pool. If it's vinyl, then there is no need for higher hardness levels (except that 100-150 ppm prevents foaming). If it's fiberglass, then there probably isn't a need either though some say a higher level protects the gel-coat. For plaster/gunite/grout, it is important to have enough Calcium Hardness (typically around 300 ppm).

It is Calcium Hardness that is relevant, not Total Hardness (which includes Magnesium in addition to Calcium). The Total Alkalinity and pH are also important. The combination of these factors (and to a lesser extent Cyanuric Acid and Temperature) determine whether the water is saturated with Calcium Carbonate. Saturating the water with Calcium Carbonate protects pool plaster as well as exposed tile grout from corrosion. Excessive Calcium Carbonate can lead to scaling so an approximate balance is desirable.

The Calcite Saturation Index will tell you if you are in approximate balance. By the way, this applies as much to SWG pools as non-SWG pools. In SWG pools one usually wants to have the index be slightly corrosive since the higher pH in the SWG cell will tend to deposit calcium carbonate, but you don't want to be too corrosive or else pool plaster can be affected.

Richard
aquila

water softened pools

Postby aquila » Thu 24 Jan, 2008 20:15

This is a pebble tek pool. normally we just test for free chlorine and PH, not calcium hardness. What should the calcium hardness reading be and would you expect it to be lower in a water softened pool as opposed to a non water softened pool?
chem geek
Pool Industry Leader
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Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Postby chem geek » Thu 24 Jan, 2008 22:42

PebbleTek should probably be treated like a plaster pool due to the concrete-like binder used to hold the pebbles together. If you raise the Calcium Hardness to 250 ppm, you should be fine, but you can use The Pool Calculator to enter in the pH, TA, CYA, CH and Temp to calculate the Calcite Saturation Index (CSI) which should be near 0 or a little corrosive, say down to -0.2 but probably not much below -0.3. In practice, problems aren't seen unless the index gets pretty far away from 0.0.

And yes, I would expect that initial pool water that came from water that went through a water softener to be VERY soft and have a CH that is extremely low. You'll need to add Calcium Chloride to raise the CH.

Richard

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