Optimum CSI value for SWCG

First, it is important to understand that optimizing your CSI is not normally important. You don't want it wildly off, but at the same time, there is no point in trying to hit some specific value exactly. The primary time you need to think about CSI is when you are unable to keep one of your levels in the normal ranges and need to compensate by adjusting your other levels. This comes up in situations like high CH fill water in arid parts of the country, where very high CH level are unavoidable.

In a normal pool with normal levels you ought to be fine if you follow the guidelines in our recommended levels chart. All that said, with plaster I aim for a CSI around -0.2 or -0.3, assuming there aren't any other constraints that push for slightly higher or lower values (like very high CH, or lowering TA to reduce PH drift, etc).
 
CSI will vary with temperature and pH, both of which cannot be that easily controlled precisely so to try and hit an 'optimum value' instead of keeping it in range is not really possible. (For exanple, temperature in a pool is not constant throughout the entire pool at any given point in time so the CSI would vary depending on the part of the pool you are measuring.)
 
I realize that pH and temperature will vary, however in most cases they will vary by limited amounts on a daily or weekly basis. For example pH, if the pool is being maintained on a regular basis, then the pH will not wander outside of a very small range. After all that is why we test the water. Like wise the water temperature. This will vary seasonally, however on a daily basis, the range of temperatures will not be that great.

What I am getting at, knowing the water parameters, I choose a target pH that will set my CSI. I have an acid pump so typically my pH will not vary by more than 0.1 pH in a week. Each week when I have a new set of test results, I calculate a target pH that will give me my desired CSI.

In any case I am one of those people that have hard fill water so have high CH. I have been processing the water to lower the CH, which is working, and I have noticed that my target pH is also rising. At this point with a CSI of 0, my pH is at the upper end of the range.
 
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