With my new TF-100 test kit, I've been measuring 180-190 CH. I'm wanting to target around 300ppm, so I bought 15 lbs of calcium chloride. According to the label, 4 lbs in 10k gals equals +40ppm, so that would mean that 15 lbs in 25k gals should equal +60ppm. I added 5 lbs last Fri morning, 5 more Sat morning, and 5 more Sun morning. Last night, I tested the CH, and it was 210ppm. Notwithstanding operator error, what is going on? I'd like to discount operator error b/c this is a simple test that I feel confident with. I assumed that 3+ days was enough for all of the Ca to dissolve.

Phillip

5 lbs of calcium chloride would only raise the CH in your 25K gallon pool about 22 ppm.

It's much easier to figure these things out by using the Pool Calculator. There is a link to it in a my signature line. Click on it and bookmark it on your computer. At the bottom of the Pool Calc page, there is a section that allows you to see the effects of adding certain chemicals. Very useful.

I would try the pool calculator and see what it tells you to do. Put in what your starting was of 190 and then put 300 as the goal and see what it says to add. Then subtract what you have added already from what it says and see what happens.

Have you used the pool calculator before?

257WbyMag and I posted at the same time.

The pool calculator gives the same answer: in 25K gallons, 15 lb would add about CH 65. So that should get from 180-ish to the 240-250 range. Why is it only 210? Could be a couple of reasons. Maybe the stuff isn't really 100% calcium chloride; maybe it didn't really mix thoroughly (have you brushed the pool?); maybe the pool volume is a little higher than you thought; or operator error on the CH test, which people do sometimes have trouble with.

Pool Calc suggests that getting from 180 to 300 requires about 25 lb total. I would go ahead and add the remaining 10lb, then see where that gets you.
--paulr

PaulR is right. I miscalculated it.

"Proper" water chemistry levels for a gunite pool is 200-400 ppm CH. 300 would be smack in the middle of the range, but I am wondering why you picked that level?

Down here in my part of the Country we would love to have 200 ppm water!

Thanks guys. I do use the Pool Calc often. It's great. That's where I started from and how I knew that I could add the full 15 lbs and then re-check. I just happened to quote those numbers b/c that's what the label on the back of the container said. It's hard to argue with the label on a product. I used "Balance Pak 300". Pretty sure it's 100% calcium chloride.

My pool might be slightly off from the 25k gals, but not nearly enough to cause that disparity in my results.

Good point about brushing the pool. I've always done that with calcium and salt additions, but I didn't this time. This year's version of Balance Pak 300 is much closer to a powder than previous versions (large chips). After I dumped it all around the deep end, I honestly didn't even see anything on the pool floor. I'll brush to be safe.

I picked 300ppm for several reasons. One is that it's in the middle of the ideal range as you said. Another is that the CH factors into the CSI calculation, so it's one "knob" you can turn to tune the CSI. In my pool, the other components of CSI push my water toward corrosiveness, so I want to use CH to offset that.

PaulR, just to follow up, I brushed the pool and waited a couple of more days, and the CH is now reading 240 as we expected. Thanks.

Excellent! Probably some of it was just sitting on the bottom. Glad to hear it was really that easy!
--paulr