If you are referring to 'Safer Muriatic Acid' by WM Barr sold under the Kleen-Strip brand and/or "Acid Magic" by certol then these are 'buffered' muriatic acid products that contain 'propriatary' ingredents to reduce fuming and irritation to healty unbroken skin. While Acid Magic is listed on the manufacturer's website as suitable for pool/spa pH adjustment use the Safer Muriatic Acid is not.
While these products claim to be as effective in cleaning as 20 baum muriatic acid they do not claim that they ARE 20 baum muriatic acid and the MSDS for both indicate that they are actually much less concentrated that standard 20 baum muriatic acid.