You won't see any change in pressure -- I presume you are adding it directly to the bulk pool water. What you add to water is like adding salt -- it fully dissolves. It does have a small effect on Total Alkalinity -- 50 ppm Borates at a pH of 7.5 increases TA by about 5 ppm -- but you can use The Pool Calculator to calculate the saturation index and it will account for the Borates (assuming you put that into the calculator).