Tomab Posted October 27, 2011 Report Share Posted October 27, 2011 I've been using the dichlor/bleach method with great success. No problem with that. The question I have is how important is the Saturation Index in a acrylic, non-plaster/non-concrete hot tub? I have read conflicting opinions. Some saying it's only important for the plaster or concrete pool. Others say you should watch it in both hot tubs and pools. The reason I am asking is I am working on balancing my tub water after a water change. I have the water parameters all within the "normal" range except for the Saturation Index which reads a -.3. I understand anything in the .5 thru -.5 range is supposed to be ok but I feel I'm being compelled to try and get the SI as close to "0" as possible. Should I be attempting to do this in my acrylic hot tub or am I wasting time and chemicals? I've never really paid attention to SI in the past but I do want to balance the water correctly. Thanks, Tom Quote Link to comment Share on other sites More sharing options...
chem geek Posted October 27, 2011 Report Share Posted October 27, 2011 Don't worry at all about the saturation index for an acrylic spa. It's only if it is high where it might be a problem for scaling, but in your situation this is not a problem. You only need the CH up at 120-150 ppm if you find problems with foaming. Quote Link to comment Share on other sites More sharing options...
waterbear Posted October 27, 2011 Report Share Posted October 27, 2011 Saturation index, as it is applied to pools and spas, can only predict how likely it is for calcium carbonate (scale) to precipitate out of the water or how aggressive the water is to plaster (calcium) surfaces. IT has absolutely NO bearing on metal corrosion. As a predictor of scaling conditions the most important factor in the SI equation that can be controlled is the pH (second most important is temperature, which we really cannot change or we won't have a hot tub!). Therefore, by monitoring the pH you can help prevent scaling conditions. Since there are no plaster surfaces in an acrylic spa then SI is not really something to worry about unless your fill water has very high calcium hardness. To make things easy if you keep your pH below 7.8 for chlorine or 8.0 for bromine, and your TA below 80 and you should have little worry about scaling if your calcium hardness is below about 300. Quote Link to comment Share on other sites More sharing options...
Tomab Posted October 27, 2011 Author Report Share Posted October 27, 2011 Chem geek and Waterbear. You guys have been an enormous help for me over the last few years. Thanks for setting me straight on the SI. Tom Quote Link to comment Share on other sites More sharing options...
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