I am one of the operators of a commercial facility, with a lap pool holding about 250,000 gallons. The source water has 150ppm total alkalinity, but our pool consistently hovers around 40-50ppm TA. This is with regular addition of sodium bicarbonate (over the last month we added a total of 150kg sodium bicarb, which did nothing but hold the alkalinity steady at 40ppm). We feed gas chlorine and keep it around 1.0ppm free chl2 (~1.2ppm total), and supplement with a slipstream O3 system. Our pH holds quite steady between 7.4-7.6, and the temperature is 27.5 C. We very rarely add small quantities of muriatic acid to lower pH, and feed soda ash automatically to maintain a 7.4 set point. No other chemicals are added.
My question is why our alkalinity is so low, and why it is so difficult to raise it. Also, I wonder if there are any issues with just leaving it at that level, given that our pH is stable. Any ideas?