CH going up fast again

[Aqua Woman]

We built our gunite pool in spring of 2018. Our CH has always been on the high side, and inched up close to 1000 ppm towards the end of this summer. At Thanksgiving (a bit over two weeks ago), I did a water exchange (tried to do 80% exchange, but wasn't too sure how much I actually exchanged). I tested my source water and found pH 8.2, CH 150 ppm, and TA 220. I've slowly been rebalancing chemicals (added a little too much salt although I was following Pool Math). I will find the sweet spot again for TA vs pH, but what concerns me is why my CH is already at 500 ppm again? I have added no water, and it doesn't even look like the water level has gone down at all, very little evaporation. (The pool is enclosed in a solid-roofed, screened pool house). Where is all the Calcium coming from? I only added salt (food grade from the pool store), Muriatic Acid, and Home Depot liquid bleach after the exchange.
Latest test results: FC 3.0, CC <0.5, pH 8.7, TA 140, CH 500, Salt 3600, Temperature of pool 63 degrees, CYA 0
Thank you

 

[mknauss]

Your exchange may not have been very efficient. Or you did not exchange as much as you thought. Did you do a flow rate test during the exchange to see how long to run it?

 

[Aqua Woman]

My fill rate was only 6.5 gallons per minute, so I calculated it would take something like 35 hours to do the exchange. The problem I ran into was that the sump pump was way more efficient at draining the water, so I had to turn it off three or four times during the exchange. I was hoping it wouldnt matter all that much. I had the sump pump in the deep end, and the fill hose in the basket so it wouldn't disturb the water too much. But even if I didn't achieve a very complete exchange, why is it going up? Shouldn't it hang out around the 400ppm mark where it was immediately after the exchange?

 

[mknauss]

You are correct. It should not be increasing much this time of year.

Test it every couple weeks for a couple months and see if you see a trend.

 

[Aqua Woman]

Since I live in SW :Louisiana we don't close our pool for winter. I check things at least once a week even in cold weather. We have never had any algae or cloudy water issues. Just a high CH which of course messes with the balancing of things. But I'l be back on here in a few weeks........, I have a feeling.