Sudden CH rise


Well-known member
Jul 17, 2007
North Texas
On 5/29 I ran my first tests with the tftestkit. My one year old pool is approx. 25k ING saltwater. I also had Leslie's run a set for comparison on the same day. My numbers are in the first column.
FC 3 3
TC 3 3
PH 7.6 7.8
TA 110 100
CH 360 350
CYA 30 60
Borates 40
Salt 3200 3200
Temp. 84

I added 4# CYA, a bag of salt, and 4 boxes of borax. Not all at once! I added acid to knock back the ph. My next TA and CH were 130 and 550 respectively. After adding a half gallon of acid the TA is down to 90 (ph 7.2). I'm now aerating to get ph back up so I can drop the TA some more. What I don't understand is the sudden rise in CH. We did get 3 inches of rain between these tests. Although we've had bigger storms than that in the past year. We are also seeing white flakes of what I presume is scale in the cleaner screen and debris. Now the IC40 cell light is flashing and not making Cl. I've cleaned the unit 3 times in the last year and every time there was minimum bubbling on the plates. Visually I couldn't see anything on them. The unit has performed w/o issues until now. Since I'm currently out of town I'm my wife will have to do the cleaning. My filter is running 0# psi (which is normal at my pump rates when it's clean). We're using bleach for sanitizer. My CYA is now 47. I plan to eventually get it close to 80 per Pentair's (and this site's) recommendation. So far we haven't been seeing flakes anywhere else. I'm hesistant to replace water to lower CH until I know what's causing it. This is the first issue with the water since we got the pool. We have city water for fill. The only chemicals I have ever added are salt, bleach, borax and muriatic acid. I'm wondering if the self cleaning mode has failed and Ca has precipitated out. Any ideas?


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
My filter is running 0# psi (which is normal at my pump rates when it's clean).
Your guage is broken...I'd get that fixed so you get meaningful readings.

I'm somewhat unsure about your CH. Unless your fill water (have you tested it?) is incredibly high, the CH cannot get into your pool on it's own.

You are certainly on the high side of normal for CH and, if you've allowed your pH to slip up above 7.8, that could be your issue. Do you think that during this "lowering Alk" phase, that could be the case?
How low did you drop your pH? You very possibly dissolved some scale which would cause the CH to rise. Just continue to lower the TA a bit lower than you inteneded to compensate for the higher CH and you will be fine. (and keep close watch on your pH to keep it from going about 7.8. )