If your CYA is 100, your chlorine level should be between 8 and 15. If your OTO test goes to "5", you can dilute pool water with steam distilled water 1:1 and "5" indicates a chlorine level of 10. I like to use a shot glass to get equal amounts to mix.

If you need to go further, 2 shots of distilled to one shot of pool means a reading of "5" on the OTO scale is really 15.