If you've had your pool for some time now, doubtless you understand the importance of some key chemicals in your pool – namely pH and chlorine (or whatever other choice of sanitizing chemical you use). Although these two readings may be at the top of the list to maintain, there are other levels well worth monitoring and keeping up on so as to protect your pool’s components as well as swimmers. Calcium, often referred to as calcium hardness, is one of those chemicals that could be easily ignored, at first giving the appearance of little importance only to haunt the pool owner in the long run with serious costly damage.

Some years back in the early days of my career in the pool and spa business I worked for a retailer (whose name I will not mention to protect the innocent!) that sold a lot of pool chemicals, but generally by accident. I say this because, the company taught the employees how to test water, input the results and explain to the customers what they needed, but often did not explain why they needed the chemicals we were trying to sell to them. This was the case especially with calcium hardness in that we would tell our customers how much they needed, but had little idea why it was needed. The end result of this lack of understanding was that both customer and employee ended up feeling as though it was a snake-oil product – “you just need it because we say so”. I remember one woman, after having told her that she showed almost no calcium in her very large in-ground pool and would need almost 40 pounds of calcium, asking me in a whisper, “Do I really need this? I’ve never put it in my pool before.” Unsure of myself, I remember telling her not to worry too much and she went to the register without the calcium. This was one of the moments that I realized I needed a better understanding of pool water chemistry and the products available. Now countless thousands of customers later, I wish I had the opportunity to speak with that same woman and give her the correct, important honest information.

The analogy that comes to mind for neglecting calcium levels in a pool is one of driving your car every day, filling the tank, and keeping the car looking clean externally, but never changing the oil. Go a couple hundred miles after when your car is due for an oil change – net result, no big deal. A few thousand, you may get away with it still. Continue this and you’ll inexplicably have a car that is run into the ground at 50,000…60,000 (or so) miles. It’s a slow cumulative effect. Calcium in your pool is similar to the car analogy. Neglected calcium levels in your pool often are low, but can be skewed high as well if you’re not doing some routine monitoring.

Low Calcium Levels in the Pool

Calcium on the low and high end of the scales will eventually cause problems and when they do, be ready for some serious problems. Low calcium, as is often the case, will cause long-term serious damage especially to plaster, vinyl liners, grout in between tiles, metal rails, and even concrete decking around the pool. Here’s why it happens. Plain old water, believe it or not, is very aggressive. By that I mean that water seeks to dissolve and bring into solution minerals, metals and other substances. Although soft water is desirable in everyday home use, calcium hardness is necessary in pool water. With sufficient levels of calcium dissolved, the aggressive nature of water is tamed and will help prevent the leaching out of certain substances in pool equipment. Low calcium levels in a plaster pool will cause the water to draw calcium directly from the plaster, causing it to pit, become rough, and eventually crumble. If you’re faced with a re-plastering job on your pool you’ll realize that this is a HUGE expense and a very big hassle. Low calcium also contributes to vinyl pool liners losing their elasticity and supple nature. In short, it’s a great way to shorten the life of your liner!! Metals (everything from rails, to heat exchangers on heaters) will corrode slowly, and you can multiply this effect even more if you let the pH of you pool plummet and stay low for long periods of time. This is starting to sound like the car needing the oil change, huh?

High Levels of Calcium in the Pool

Excessively high levels have adverse effects too, though. Scaling (that does not come off of the walls, and equipment easily), cloudiness that will not change, and even irritation to eyes and skin can occur with calcium levels above the desired range. What happens in this case is that there is simply too much calcium for the water to hold in solution, and it begins to come out of solution causing cloudiness that will NOT subside, and leaving excess calcium in the form of scaling. It will even slow down your filter system in many cases because it begins to clog the filter and limits the rate at which water may flow. High pH will compound your problem as well, since higher pH allows for more substances to come out of solution and adhere to the pool’s surfaces.

Calcium is one of the few chemicals that you do not want to put in a little extra for good measure. Once levels are too high it generally does not leave the water and needs to be drained partially and have fresh water added to dilute the concentration. With this in mind don’t be paranoid, but test your water at a trusted professional pool expert and add only as needed. The good news about calcium is that once established at acceptable ranges (often in the beginning of the season) it will generally remain constant throughout the season and possibly into the next year. See your local water professional, but generally calcium levels in the range of 200 to 400 ppm (that’s parts per million) is where you want to be.

So check those calcium levels, adjust as needed, avoid expensive repairs and... oh yeah, keep swimming!

If you have any questions or would like to learn more, our team at EZ Pool & Spa Supply would be happy to assist you!