Salt System newbie

[chem geek]

If you find that the pH tends to rise over time and if your pool is exposed to direct sunlight, then having the CYA in the 60-80 range, especially 70-80 ppm, has the chlorine protected more from breakdown in sunlight. Even proportionately raising the FC level to 4 ppm minimum with 80 ppm (for an SWG pool), there is less absolute chlorine loss.

The lower chlorine loss lets you turn down the SWG on-time and that reduces the rate of pH rise (from whatever the cause -- could be more outgassing of either carbon dioxide through aeration or of undissolved chlorine gas).

Adding 50 ppm Borates can also help reduce the rate of pH rise through two effects -- it acts as a pH buffer and it is a mild algaecide so may further reduce daily chlorine usage. It's also insurance since at the higher CYA level you want to make sure you don't have the FC drop below the minimum since fighting an algae bloom takes a lot more chlorine (higher FC level) when the CYA level is higher.

As for eyes burning at 100 ppm CYA, that probably wasn't a direct result of the CYA but the FC probably wasn't high enough (i.e. was below 5 ppm) and that meant that the active chlorine level could have been so low as to have more chloramines in the pool and those can be irritating to the eyes. Either that or the pH may have been off (too high or low). If you find any problem at 80 ppm CYA with 4 ppm FC, try increasing the FC target to 6 ppm, but I doubt you'll need to do that since there are many, many people with SWG pools that mostly operate with 4 ppm FC and 80 ppm CYA without any issues.