Balancing Colder Water


Active member
Sep 10, 2019
Houston, TX
Hi all,

Our first pool was finished last spring so this is the first "Texas winter" that I have dealt with pool-wise. I had pretty good success with the pool over the summer, but things seem to be going a bit haywire now that the water temp is dropping. All summer, my numbers looked mostly like this:

Water Temp = 66F
pH = 7.4-7.5 (31% muratic)
ORP = 700 (liquid chlorine)
TA = ~100 (use baking soda)
CH = 200-220 (CaCl2 salt)
CYA = <35

I have an IntelliChem system for pH and ORP (I know that the feeling here about these systems on here, but it works for me :)). The system measures LSI and I strived to maintain it as "balanced". My LSI was usually negative, running between -0.3 and 0. As I said, this all worked until water temp dropped. I having a bit of trouble controlling TA (dropping) and CH (dropping) and it seems like I am adding more acid than usual. That makes sense, but I cannot figure out why. It has rained a few times and this is the only thing I can figure out that would be causing it. After each rain, I check the TA and add baking soda but it still seems like it continually drops. I cant figure this one out. I do have a pool filler which is connected to the house supply which runs through the water softener, so if I have a leak there that is the other option. Any ideas?

I am also curious where you recommend to run TA and CH in the colder weather to help prevent the corrosive water. I have been playing with the calculators and it looks like I need to be running my TA and CH on the high side of the ranges (TA = ~120 and CH = 330-350) to keep the water balanced down to ~40F. I am not sure how far the water temps will drop here in Houston, though I cant see it getting much colder than that. My pool will not be covered over the winter. Recommendations?


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

My first thought is why are you trying to keep your pH at 7.4/7.5... I believe that letting your pH come up to 7.8 and quit trying to hold your TA at a specific number will let you go down to 40 degrees with an LSI of about -.2.. A CH of 220 is on the low side, so increasing to 300, will get you to about -.07..

Water temp has a huge impact on CSI/LSI... Just letting your pH change with the water temp should make your LSI problem disappear. There is nothing magical about having a pH of 7.4... :mrgreen:


Jim R.