I usually bring a water sample to my local pool centers every couple of weeks or so, Leslie's and Oasis Pools in Charlotte. They're located approx. 2 miles from each other and more times than not, the reading printouts can vary significantly, as was the case today using identical samples taken from my pool at the same time and location in the pool.
My Leslie's reading today with their charted recommended ranges:
FAC (Free Available Chlorine) 4 (recommended range 1-4 ppm)
TAC (Total Available Chlorine) 4
Salt 2600 (rec. range 2500-3500 ppm)
Calcium Hardness (CH) 300 (rec. range 200-400 ppm)
Cyanuric Acid (CYA) 50 (rec. range 60-99 ppm)
Total Alkalinity (TA) 100 (rec. range 80-120 ppm)
PH (PH) 7.4 (rec. range 7.2-7.8)
Phosphates (Pho) 300 (rec. range 100 or lower)
My Oasis Pools reading today with their charted recommended ranges:
FAC 0.5 (rec. range 1-3 ppm)
TAC 3.0 (rec. range 1-3 ppm)
Salt 2800 (rec. range 3040-3520 ppm)
Calcium Hardness 280 (rec. range 200-450 ppm)
Cyanuric Acid 100 (rec. range 20-100 ppm)
Total Alkalinity 60 (rec. range 100-150 ppm)
PH 7.4 (rec. range 7.2-7.6)
As you can see, there's a big discrepancy in the respective FAC and CYA readings. The salt reading per my PDA was 3000. Oasis doesn't test for phosphates, and, from knowledge obtained from different sources, including this site, phosphate level isn't of much significance if the chlorine levels are sufficient and the water is clear. As I mentioned, the variance in the two pool stores is a usual thing, albeit the inconsistency is quite perplexing and frustrating. However, the discrepancy is usually in the not so critical category as the FAC. l
Since Oasis Pools was the later test, and where the low FAC reading resulted, I was strongly instructed to shock the pool. Since I hadn't shocked the pool most of the summer (thought there was no need to since the water has been clear all summer) and when testing with my Pentair Kit where you place 5 drops of applicable solution into particular vile section to check chlorine, PH, etc., the chlorine has generally tested dark yellow, so at least 3, I was a bit taken aback. Therefore, I purchased a case of their "Punch" and shocked the pool this evening. I added 6 lbs. of the recommended shock based on Oasis' advice. The Oasis person also told me that those kits that test for chlorine are deceiving as it doesn't test for FAC, but rather TAC. She advised that's why the water needs to be professionally tested for FAC!
As has been the case all summer, my pool water was crystal clear today...and at the time I added the shock this evening. Additionally, in the 2 years since my pool was built, I've never had any visible algae, and the water has always been clear to crystal clear.
I have the SWG set at 60%, which has been the norm during the summer months. My water temperature is currently 90 degrees...the pool is in full sun from mid to late morning until about 4 p.m.
Thanks for any replies!