Calcium Hardness Public Service Announcement


Jun 27, 2016
Osawatomie, KS
My CH numbers have been a little low, around 200 in my vinyl pool. I know that CH isn't as important in vinyl environments where (high ppm) scaling or (low ppm) erosion aren't big concerns, but what I have learned is that CH is VERY important to water stability and saturation in ALL pools. The higher the CH number, the more stable the Saturation Index is. If you have a good Taylor test kit and have a Water Balance (saturation index) wheel, you can see that a 100 ppm difference of CH between 400 and 500 is a much smaller adjustment than the 100 ppm between 100 and 200. Since splash out and rain water continually dilute the pool water readings, I wanted to pump it up to something closer to 400 in my pool.

But "CH increaser" is STUPID expensive. It's a simple chemical, Calcium Chloride, that the pool companies market (read: hype and overprice) to the unsuspecting and naive. Thanks to the fine folks here at TFP, I leaned that I could buy Calcium Chloride ice melt at my local home improvement store for CHEAP. (NOTE: There are a ton of ice melt blends out there. You are looking for something that says Calcium Chloride; NOT rock salt and NOT a blend. It is important that you read the label on the bag.) I looked on line and found some at a nearby Home Depot, $19 for a 50LB bag. The first problem I had was that this product is in deep storage in July. They have it inventoried and palletized, out in the garden area, waiting for next winter. They also don't want to get it down for you to buy 1 bag. But they did, after a talk with the Store Manager. (Thankfully, I didn't have to go full crazy on him.) The second problem I had is that this stuff is 90-92% CC pellets, while "CH increaser" is usually always 77% flake. Pellet vs flake is no big deal, pounds are pounds, but the new dosage amount for a 200 ppm increase was difficult to measure, as nearly all pool calculators are set up for the 77% stuff. So, I did my best math adjustment, and decided that adding the full 50lb bag was not going to get me in trouble.

I learned a couple of things: One, it takes a couple of days for the CC to fully dissolve and distribute through your pool. I was happy with the readings I got the morning immediately after adding, but was really surprised with my day 2 reading, measured at 530ppm! I measured it 3 times, to be sure it was not my error. The second thing I leaned is that 530 is no big deal, and not to flip out about it. I read than many pools run numbers as high as 800 or even 1000 ppm without trouble, as long as the other parameters are in check and the saturation index is happy. As I said earlier, I know that the CH number will slowly creep downward through the season, and will really drop off next spring after the pump down and refilling the pool after winterizing.

I'm not going to worry about it. My Saturation Index is a +.20. I'm going to throw a little muriatic acid in the pool and bring the ph down a little to 7.2. That will get me under +.10. My goal is to stay between -.1 and +.1, while my SWG manufacturer is happy with anything between the -.20 and +.20.

Hope this helps some of you. I read a lot of threads where people freak out when something gets out of whack, and there was a time when that applied to me, also, but I have learned that knee jerk reactions to pool maintenance are often unnecessary and ALWAYS costly.

Sandrat from Kansas


Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
Tucson, AZ
So, I have to agree with Marty on this. There was no good reason to raise your CH. A low CSI does not mater in your pool, but a higher one can still cause scaling, especially in a SWG. For a SWG, we recommend keeping the CSI between -0.3 and 0 ... ideally never on the positive side. Now that you have raised your CH so high, that means you need to try to keep your pH and TA lower to keep that negative CSI. And remember that the lower you try to keep the pH, the faster it tends to want to rise, and a SWG also drives the pH up. It will not stay at 7.2 for very long at all.

I think you would have found more stability if you left your CH low and then were able to keep your pH on the higher end of the scale.
Maybe you can try that next year.