As long as you have been getting decent efficiency in your mash, I wouldn't worry too much. Palmer states 50-150 ppm is your target range. Calcium is important for many aspects of the process -- enzymatic conversion, yeast health, flocculation, etc. I am no expert, but i think 43 ppm should get it done. I have seen no differences in conversion efficiency using anywhere between 45 and 200 ppm in my brews, though I did have problems when I used to brew with only ~20 ppm, before I understood water adjustment.