It does not raise CYA, but does raise CH for a 27K pool assuming no splash out or overflow from rain it will raise your CH by roughly 100 ppm (assuming this is a typical 50 pound tub), this is of course in addition to however much your CH is raised by replacement fill water and concentration of CH through evaporation. There are many locations in the west with fill water that is already over 400 ppm CH, and in general CH of over about 800 requires careful control of CSI to avoid scaling, so a lot comes down to how much CH is in your fill water, and how much water you have to replace due to evaporation where you live.