Based on the CYA to free chlorine dose ratio of 7.5 per cent, it is conceivable that the standard of 2 to 4 ppm may not be enough.
Managing the CYA is another way to use less chlorine. At a CYA level of 30 ppm, it will take only 2.25 ppm of residual chlorine to keep the pool free from bacteria and algae.
CYA to free chlorine ratio – 30 x 7.5 per cent = 2.25 ppm
At a CYA level of 100 ppm, it will take 7.5 ppm to keep the pool free from bacteria and algae. High CYA level is one of the biggest ways that chlorine is wasted.
100 x 7.5 per cent = 7.5 ppm
Also, it is important to see here that at a CYA level of 100 ppm, one must exceed the EPA maximum allowable free chlorine level to keep pool water safe. Obviously, in public pools this would be of concern. This is why the standard recommendation of CYA at 30 to 50 ppm is so important.
Managing total dissolved solids (TDS) is also key to stretching chemical use in pool water. That said, pool pros should be testing for TDS at least three times a year in a residential pool. Further, one should also know what the TDS of the source water is. The reason this is so important is because if the TDS of the pool water is 1500 ppm over the source water, then 50 per cent of the chlorine being added to the pool is being wasted. The buildup of solids in the pool makes chlorine less effective. Regular dilution of the water can help to save on the amount of chlorine that is needed to keep pool water sanitized.
Borates are also great for helping chlorine to be more effective. With a level of borates in the pool at 50 ppm, one can use half the amount of chlorine that would normally be needed. If the pool water’s free available chlorine runs at 3 ppm, it can be cut in half to 1.5 ppm by using borates. Also, using borates at 50 ppm reduces the CYA to free chlorine ratio from 7.5 per cent to five per cent. For example, if there is 100 ppm of CYA, one would need 5 ppm free chlorine.
100 x 5 per cent = 5 ppm
