OK Pool Experts...just need your thoughts on this.
I'm dealing with a commercial customer in the Long Island area, 140,000 gallons, Sand Filter, CYA = 10 ppm, TA = 0 ppm, CH = 60, pH = 7.4. New York State does not allow stabilizer in commercial pools, except with a waiver.
They have the Pool Pilot Professional system, with an output of 30 lbs/day maximum, and we're running every ounce of that 30 lbs/day! Water looks great. They're just able to maintain a decent chlorine residual (5 ppm) without adding gobs of sodium hypochlorite in addition to the Pool Pilot system running full tilt!
So, I determine that they have a heavy chlorine load since we're not able to keep up with a 5 ppm FC level, and I suggest that they shock the pool and run an overnight chlorine drop test.
It dropped from 30 ppm to 12 ppm overnight. Ta Da (I thought). Let's shock it again....same results. On the third shock dosage, this weekend, we went from 40 ppm to 31 ppm (Friday to Saturday 4pm), and by Sunday morning, down to 25 ppm. Today, we're back down to 12 ppm.
What am I missing? We've dosed almost 75 gallons of sodium hypochlorite (pool store strength - 10 - 12%), 3 times.
Keep in mind that the pool water is rather cool, 68 degrees, and there has been NO swimmer loads.
I don't think the sand filter has been recharged with sand in many years, and I hear there is a daily heavy MICE KILL load in the skimmer, which I'm sure ends up with some level of organic load in the system.
I'm actually going to be on site tomorrow (Tuesday) and they are asking, "What now?"
I think we're almost overcoming the heavy chlorine demand condition and would like to see them shock it one more time. Do I recommend sand replacement too?