If a pool is saturated with calcium carbonate, which plaster/gunite pools should be (or pools with tile that has exposed grout), then adding sodium carbonate / pH Up / Arm & Hammer Super Washing Soda may cloud the pool or cause precipitate if added too quickly. The same is true if one adds Cal-Hypo. To avoid this, pre-mix these products in a bucket of pool water and slowly add them.
Also, get a good test kit, the Taylor K-2006, and test the water yourself. It is possible that you have a combination of too high Calcium Hardness (CH), Total Alkalinity (TA) and pH which cause over-saturation of calcium carbonate and cloudy water. Lowering any or all of these is usually the answer, though CH can only be lowered by dilution while TA requires aeration at low pH as described in this post