sudden drop in CH and best remedy

[NSBFAN]

Hello everyone. It's been cold here in FL and we've had a lot of rain and storms lately. Since last week, I got 2-3" of rainwater into the pool. My CH has dropped down to 220. My readings today:
FC - 9
CC- 0.0
PH - 7.7
TA - 70
CH - 220

That seems to be under the 250-350 range for a plaster bleach pool. Should I bring that up and if so, use just calcium chloride or that plus baking soda?

 

[Texas Splash]

From the Pool School - Recommended Pool Chemicals page:

Calcium hardness can be raised with calcium chloride or calcium chloride dihydrate. They are available in some areas as Peladow, Dowflake, Tetra Flake, or Tetra 94, often sold as a deicer by hardware stores, and some big box stores, in colder climates. Pool stores will carry either calcium chloride or calcium chloride dihydrate under a variety of names, including Hardness Plus, Balance Pak 300, Calcium Hardness Increaser, etc. Calcium products should be spread across the surface of the deep end of the pool.

 

[JVTrain]

I wouldn't add CH at this stage. Just allow your pH to live at 7.8 or even near 8.0 for a while, to keep your CSI neutral. Right now you're at about -0.4. This is still a fairly safe spot to be, leaning toward the corrosive side on your plaster. At pH= 7.8, -0.3 CSI, at pH = 8.0, -0.1 CSI.

CH has a tendency to rise on its own, unless of course you're always getting lots of rain (low CH fill).

If you drop any lower, toward 200, then I would consider raising it, only because you probably get lots of rain and may not have to worry about rising CH, like someone in say Phoenix would have to. Use only calcium chloride to raise CH. Baking soda will raise your TA and yours is great right now.

 

[NSBFAN]

Thanks! My CH had been real steady since I started doing TFPC method and using the poolmath calc and great info here. I hadn't seen it rise before.

I forgot to mention my pool temp is chilly - 60% right now. When I used my Taylor K2006 Watergram calculator, I got an SI of about -0.15. Pool Math shows -0.4 like you said. I wonder why the difference?

 

[Patrick_B]

Because Pool Math uses CSI instead of LSI. CSI is better or more pertinent actually for pools.

Generally, it's best not to get hung up on CSI unless there are extenuating circumstances. As JV said, not too concerning, and he covered it well.