Is CSI a long term problem or a short term problem


Active member
Jul 8, 2015
San Antonio, TX
I feel like I'm always working the edges of the allowable CSI levels. How much should I be worried about CSI? Is it a longterm neglect problem, or can limited time at or beyond the acceptable limits of CSI be harmful as well?

Here are my test results:

PH - 7.2
FC - 8
CC - 0
TA - 100
CH - 250
CYA - 50
NaCl - 1000
Borates - 15
Temp - 72
CSI = -.49 (potential to become corrosive to plaster)

I'm currently trying to lower my TA a little so I can add borates. That is why my PH is at 7.2. I have a waterfall so I'm always fighting rising PH. My fill water is also high in PH and TA so I keep MA on hand at all times.

Pool looks great. I'm actually using the heater to warm it up a little for swimming this weekend.



LifeTime Supporter
TFP Guide
Jun 12, 2011
While I'm in the process of lowering the TA I often reach that kind of CSI and even lower. It doesn't stay there long, just until the aeration raises the pH. There is no cause for concern. Your pool won't dissolve overnight. In fact PoolMath lists the acceptable range as between +0.6 and -0.6, so you are comfortabilty within that range.

When lowering my TA, I find that I get the best results by lowering pH to 7.0 then letting it rise to 7.5 before lowering again. That seems to work the quickest. Good luck with getting the pH to stabilize. I fight pH rise constantly. High evaporation, high TA fill water and SWG.


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
Aug 10, 2012
FL panhandle
Yes, agreed you are doing fine with your CSI and working on lowering your TA. If your heater has a copper heat exchange then be careful with pH below 7.0 for longer periods of time. Low pH will dissolve copper into the water over time. Keeping it 7.2 is safer.

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