Parrick Posted April 9, 2013 Report Share Posted April 9, 2013 After reading some of the posts in the forum I learned that the "recommended" TA for my swim spa (80-150ppm) was way high & led to the need to constantly add acid to lower the pH. After some experimentation I found that a TA of 40ppm results in a very stable pH which will hold steady at 7.6 for up to a week or more. If the aerators are used it will creep up slowly & can easily be corrected with a small addition of dry acid. If I notice a trend in the pH creeping downward I know to test the TA & bump it back up a bit with some baking soda. This method has greatly reduced the amount of time & reagent that I use in maintaining chemistry. It is also nice to know that I can bump the FC up to 5 ppm or so & go on vacation for a few days without having to worry about the spa chemistry getting all out of whack & coming home to a disaster. My only concern is this: When I enter my numbers into the Pool Calculator I end up with a resulting CSI of -0.42. The Pool Calculator indicates that this has the "Potential to become corrosive to plaster". I am assuming that this is not an issue with an acrylic spa with stainless steel parts. Am I correct? Is there any downside to my method? My numbers are as follows: Size 1525 gal FC 3 pH 7.6 TA 40 CH 150 CYA 26 Salt 26 Borate 0 Temp 95 F CSI -0.42 Quote Link to comment Share on other sites More sharing options...
chem geek Posted April 10, 2013 Report Share Posted April 10, 2013 You are correct that with an acrylic spa there is no problem with the negative CSI. As for metal corrosion, low pH would be a problem, but not low CSI itself. Quote Link to comment Share on other sites More sharing options...
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