Swimming Pool Water – Hard or Soft?

POOL BW4As we head into hot summer days the swimming pool becomes a big target for our cannon ball jumps and squish-ball wars. Water splashing everywhere; Into our ears, eyes, mouth, nose, and even poolside food and drinks. Nowhere is an understanding of water chemistry, biology and physics more important than in our swimming pools. The subject of pool water management is far to complex for a single blog post, but for today let’s talk about hard water versus soft water in pool water management.

For this discussion we will confine the conversation of hardness only to the element Calcium (Ca).  Ca is a very weird element because unlike many other metals it actually becomes more likely to form a precipitate (scale) as the temperature rises. Since pool water is warm, and since evaporating water causes pool Ca levels to rise, there is always the tendency of hardness to cause water to become milky or cloudy. If you have ever seen pool water like this, what you likely were looking at was calcium precipitate contaminating the water.

Pool F DiverSo does that mean pool owners should purchase a water softener and change all that nasty Calcium to Sodium? Well, not exactly. Soft water is chemically aggressive. It likes to dissolve things like pipes, fittings, glues and binders. It also causes surfaces to become slippery.

Most experts concur that swimming pool water behaves best when the calcium level is maintained between 100-400 mg/l (also called ppm). Making this even more difficult is the fact that Ca levels vary greatly between different water sources; So just like we learned in Flint, Michigan, the treatment program that works on one water, may be a health hazard on another water. So, if you had a great pool in Barberton, Ohio, don’t assume that you know what the hell you are doing with your new pool in Oxford, Mississippi.

High calcium levels in a pool can be reduced by diluting the pool with soft water. Just be careful and consult a pool water chemistry source. Low calcium levels can be increased by adding calcium chloride, but again, be careful and consult an authority.

Here’s wishing you a summer of happy water!