Quote Originally Posted by Charlie View Post
If I raise the CYA to 80 or so, then the FC can be lower? I'm concerned about getting accurate readings (sorry just part of my job in metrology - being precise in measurements). I guess I'll add some stabilizer to raise it a bit.
You've got it backwards. Carl was suggesting raising the FC, not the CYA. If you raised the CYA you'd have to raise the FC even more. I'd leave your CYA where it is and just try and target a 6 ppm FC instead of the 5 where you are now at. This will help ensure that you don't get any algae growth.

You'd only raise your CYA if you found that your chlorine loss from sunlight during the day was too high.

Richard