Low PH vs CSI

[AJB1234]

Hi TFP,

My main goal is to prevent scaling as I have a BLACK granite raised negative edge pool (water overflows on two sides). Is a slightly negative CSI the only number to be concerned about? I have read that a low PH is important for scale prevention but when I keep my PH on the low end 7.2-7.3, my CSI is too negative and the pool calc shows it's corrosive. Here are my CSI #s:

PH 7.3
TA 30 (i know this is low)
CH 450
CYA 19 (wife wants to keep this low plus this helps with making the CSI higher)
TEMP 48 degrees
SALT: None
BORATES: None
CSI -0.93

With the above #s, I have almost zero scaling but am concerned about the corrosiveness on my pool/equipment.
Even if I raise the TA to the upper limit of 90, the CSI still shows -0.40. Should I raise my PH to get a better CSI # or does this increase the chances for scaling?

Thanks All,

AJB

 

[Texas Splash]

AJB, a CSI of almost -1.0 is too low. CSI is derived from the combination of primarily water temp, pH, TA, CH. This is why some items can conmpensate for others when they get out of range. It's good you are using the PoolMath to monitor the CSI overall. Let your pH climb. As you noted, the TA is low and should be up to at least 50 as well. As long as the CSI is slightly negative (-0.1 to -0.3) you should see no ill effects from scaling.

Watch later in the year when water temps climb. The CSI will shoot-up quickly as well. Hope that helps.

 

[Leebo]

If I may ask, how did you come to those test results? Some of them look kinda weird.

 

[Bvacchiano]

I’ve now learned that when water temp is low in the fall/winter keep the PH at 7.6-7.8 and I’m fine. The other parameters have very very little weighing on the CSI.

 

[AJB1234]

If I may ask, how did you come to those test results? Some of them look kinda weird.

Thank you for your help. I will recheck the #s again (with my taylor kit). In the meantime, which numbers seem off to you? Thanks.

- - - Updated - - -

I’ve now learned that when water temp is low in the fall/winter keep the PH at 7.6-7.8 and I’m fine. The other parameters have very very little weighing on the CSI.

Maybe it makes sense to setup all the other CSI parameters so with a temp swing, the CSI stays in check. My pool temp varies by about 20 degrees and if I play with the CSI numbers I can keep CSI in check even with this much of a temp change. Thank you for helping me.

- - - Updated - - -

AJB, a CSI of almost -1.0 is too low. CSI is derived from the combination of primarily water temp, pH, TA, CH. This is why some items can conmpensate for others when they get out of range. It's good you are using the PoolMath to monitor the CSI overall. Let your pH climb. As you noted, the TA is low and should be up to at least 50 as well. As long as the CSI is slightly negative (-0.1 to -0.3) you should see no ill effects from scaling.

Watch later in the year when water temps climb. The CSI will shoot-up quickly as well. Hope that helps.

This does help thank you

 

[ajw22]

Thank you for your help. I will recheck the #s again (with my taylor kit). In the meantime, which numbers seem off to you? Thanks.

TA of 30. vs your PH of 7.3. TA of 30 is suspect.

CYA of 19. CYA tube measurements are in 10's and not that precise.

Salt none. I think you will find PoolMath now defaults salt to 1000. Every pool has salt in it even if you did not add it. If you use liquid chlorine it contains salt that accumulates in the pool water. You might want to get a salt test kit and check your precise value if you are trying to dial in a CSI.

 

[AJB1234]

So I checked the #s again using my taylor kit and it's mostly the same:
PH 7.3
TA 30 (plan to raise but need to make a trip to the store to purchase a lot of baking soda)
CH 450
CYA- 15 (this is a guess as the dot is visible using the larger Taylor sample tube that shows minimum CYA of 20- just added stabilizer after measurement)
TEMP 48
SALT: Now using 1000 but don't have means to measure
CSI -0.91

Thank you! Appreciate all your help and support, AJB

 

[duraleigh]

Your biggest issue is your CYA is wa-a-ay too low for proper pool water management. Not sure why your wife doesn't want it set correctly but you need to fix that. Should be immediately set to 30...;...60 if you have SWG.

Bring your TA up to around 60 and leave it there.

Since your primary issue is calcium scale, what is the CH of your fill water?

Use your Taylor kit for all your tests. We automatically don't trust any testing but your own

 

[AJB1234]

Thank you. I will bring the TA & CYA up. The CH of the fill water is 80. All tests have used Taylor kit. Thoughts?

Appreciatively, AJ

 

[mas985]

Curious, what is your "Autochlorination" means? If it is liquid chlorine with an ORP sensor, you don't want to raise CYA too much or it will stop working. A CYA of 30 ppm is a good start.

Also, it helps to remember that CSI is the difference between the measured PH and the calcium saturated PH so CSI changes in the same quantity as PH. For example, if you need to raise CSI by 0.25, just increase PH by 0.25.

 

[AJB1234]

Yes it's liquid chlorine with orp sensor and will keep cya at 30 as per manufacturer guidelines . Very interesting comment about csi and ph... quite helpful thank you