There are a few factors at play when deciding on a CYA level, and unfortunately it is a bit of a balancing act, weighing chlorine use vs ease of testing vs ease of attaining shock level if SLAM process is needed, etc.
This gives us an accepted range of about 30-50 ppm for manually dosed pools, some may even say 60 ppm in extreme sunbelt locations. As you probably know CYA is like sunblock, the higher the level the more effective it is at blocking the sun due to its buffering effect on chlorine, therefore reduced demand for amount of chlorine needed. From a cost of chlorination point of view it is the higher the better (at least within this range) The higher CYA levels require higher FC levels to maintain a correct balance and to keep things from growing in your pool,
From the Chlorine / CYA chart in pool school we see goal levels are:
CYA (Stabilizer) Minimum FC Target FC Shock FC
30 2 4 12
40 3 5 16
50 4 6 20
Consider the cheap, quick, easy, color matching OTO chlorine test can only read up to 5 ppm then it become obvious that in order to test that you are at correct Chlorination level for CYA above 40 ppm, requires the use of the somewhat more complicated and slower to perform FAS-DPD chlorine test, this adds to daily maintenance time, and is a factor for some people.
Then comes that Shock level number, notice that the level needed to be maintained at 50 ppm is nearly double the shock level for 30 ppm, this means if something were to ever start growing in your pool (for example you might get storm debris in the pool through no fault of your own) then the amount of chlorine that will be required for the SLAM process will be much higher, not only will the initial level be nearly double, but the total amount used will be greatly increased as well, perhaps biting into any initial savings you had in the economics of running that higher CYA level to start with.
Having said all that more people in your region will likely make comment soon.
Ike
