Calcium hardness is really important to make sure it is in check along with every other one. Calcium hardness is essentially the measure of how soft or hard your pool water is. The calcium reading you get when you test is how much calcium is dissolved in your pool water, in parts per million. Calcium hardness can also create a corrosive or scale forming pool just like pH or alkalinity can if it’s not kept in range. According to the NSPF, the recommended range is 200-400ppm of calcium.
Now let’s not get calcium hardness mixed up with total hardness. Total hardness the combination of both calcium hardness and magnesium. So if you’re testing for total hardness, often times found on test strips, you could be making some correction errors if you’re not taking that into consideration. For instance, if you test total hardness at 200ppm that means you have less than the recommended amount of calcium in your pool. So just make sure you’re not getting mixed up so you can keep your pool as balanced as possible.
So what happens when your calcium is low?
Water requires calcium. It “longs” for it if you will. So if there isn’t enough in the water it will find it. Plaster pools have tons of calcium in the mix so that’s where the water will go to find it. What will happen if kept low for long enough you’ll start seeing things like etching, pitting or even delaminating. It literally starts eating away at the surface of anything that contains concrete or masonry. So if your calcium is low in your pool, get it up to protect your pools surface!
What happens if the calcium is high?
Often times the calcium being high is the offender versus it being low. What can you see occur is cloudy water if it’s really high. Water can only hold so much of anything, calcium included. Without getting too scientific here once there the calcium has reached its limit, or saturation point, anything above that point creates calcium carbonate. This type of calcium is very visible in your water. Milky pool water could be a pool with super high calcium. It could even appear as a flaky substance in the water. Don’t get this confused with water mold though as that is a completely different situation.
The most common indicator of high calcium is scaling on the surface and/or equipment. There’s a myriad of problems from scale that could occur. It can cause circulation issues if it forms in the pipes. It can plug pool filters which keeps the water from flowing freely. It can reduce the lifespan or efficiency of equipment such as pool pumps, filters, salt cells, heaters & heat pumps, and the list goes on and on. Not to mention it creates an ugly look to your pools surface or tile lines. Calcium nodules aren’t to be confused with calcium scales. Nodules are plaster application issues and not to be confused with bad water chemistry.
How can we adjust the calcium?
If it’s high, the only way to lower it is through dilution, or a partial drain or refill. If you are going to do that first check the hardness in your fill water. If you have a reading of 600ppm and your fill water is 540ppm, then there’s really no point of wasting money draining it and refilling it. In that case, what you can do is keep your saturation index (we’ll discuss this in another episode) more on the corrosive side and also keep your pH down below 7.5. A lower pH keeps things suspended in water better to help prevent scale formation.
If it’s low what you’ll need to do is add some calcium chloride flakes to the water. If you go to your pool store and ask for calcium chloride you can follow the instructions on how to add it. Generally, you’ll want to add about 15 ounces of it for a 10ppm change in 10,000 gallons of water. So essentially you’re adding 1 pound to see that change. As always you want to wait a few hours (up to 24 hours) before retesting. The longer you wait for the more accurate result you’ll get when you retest it. You don’t want to drastically overshoot the application because then you’ll be stuck draining part of the water. I always dose in smaller increments instead of one large application.
Be careful how you treat your pool!
You also need to make sure what you’re treating your pool with isn’t making matters worse. If you have high calcium, the last thing you’d want to sanitize your pool with is calcium hypochlorite or cal-hypo for short. Every time you add that to your pool you are also increasing the calcium which only makes things worse.
On the flipside, if you have a pool with low calcium, cal-hypo would be a great choice for sanitizing the pool because over time you’ll bring calcium into range.
So that’s calcium hardness in a nutshell. If there are any questions regarding calcium please don’t hesitate to reach out to me. I am available in almost every possible way so please don’t be afraid to use them. I am here for you guys and gals.
Below is our podcast on this topic:
Also here is our YouTube video discussing this topic: