Calcium Hardness increasing for unknown reason

[JMezei]

Our CH began rising this summer (just after the pool hit its one-year mark). I had been using the hose (non-softened water) to fill the pool when it gets near the bottom of the tile line, and this was every couple of weeks since we haven’t had much rain. Once the CH got to the ~450 level, I started filling it with a hose from the bathroom sink to get softened water, but the CH continues to rise. The softened water CH is 25ppm, and I tested the chemicals against the control that is supposed to be 200ppm, but the readings were 225ppm (purple) - 250ppm (blue). (I included the purple reading because I have only ever gotten a purple reading for my pool water CH. I did discover the Taylor article that explains the fading endpoint due to interfering metal ions, and now I know how to get to the blue result, but the CH value remains the same. Just in case it’s relevant, my Culator bag is yellow, suggesting iron.)

We’ve had no rain and I’m now using the softened water; can anyone tell me why my CH keeps rising and if there’s anything I can do besides water replacement? I should also add that I do get some calcium scale on the rock wall and grout near the water spillover, but the water itself has not been cloudy, nor do I see any other signs of a problem. We run our filter pump/spillover ~8am-4pm daily.

 

[Newdude]

Are you using 'non stabilized' pucks or powdered shock ?

 

[JMezei]

Neither. I’ve only been using powdered stabilizer for awhile now, and only a few times. For chlorine, I use Walmart’s Pool Essentials 10% bleach (when they have it) or Aldi’s 6% bleach. And Blue Whale (31.45%HCl) muriatic acid from Leslie’s. Trying to use the chemicals focused on each issue I’m addressing, but not sure whether any of those might raise the CH.

 

[JMezei]

No input about what could be causing my CH to increase so much?

 

[mknauss]

It only gets in your water by adding it (product or fill water) or due to very low CSI for a long time dissolving your plaster. No other sources.

 

[TinFoilHat]

Probably your fill water. You need to do a CH test on it at your fill spigot or where the autofill is supplied by.

 

[JMezei]

I did test the fill water (softened, since that’s what I’m adding to try and reduce CH). It’s only 25 ppm. We *finally* got a good rain this week and I was anxious to check my CH, but it’s still hovering ~600. I’m only adding muriatic acid and chlorine bleach each week, so I’m at a loss as to what could be keeping my CH so high. I did see one comment suggesting that muriatic acid adds some salt; could that be the culprit or is it such a small amount as to not affect CH?

 

[mknauss]

Acid does not effect CH.
Unless you are draining water from your pool and adding softened or rain water, the CH will not drop.
Using softened water for makeup water due to evaporation simply keeps your CH from rising as quickly.

 

[JMezei]

Okay, this does make sense—I’ve only been replacing what’s lost to evaporation. Pool Math suggests that I replace 40% of my water, but I’m hesitant to do that just yet. Hoping my water stays under the suggested safe max of 650.

 

[mknauss]

You can manage with a CH of 600. This winter, when you are going to get a significant rain fall, drain the pool down a few inches and let the rain refill it. Keep doing that and the CH will come down.