There are problems with this approach. The main one is that calcium scaling is typically patchy, various spots here and there. If you lower your PH low enough to remove calcium scaling, you will also be etching plaster off of the rest of the pool, where there is no scale, as well as removing scale. You don't really get the control you need. Also, low PH can damage other parts, especially gas pool heaters. Never attempt this if you have a gas pool heater. You also end up with lots of calcium in the pool water, which must then be replaced, or you will just have scaling all over again.
To effectively remove scale, CSI needs to be -1.0 or lower.