I agree with mad...once it changes colors slightly that's the number. This post made me realize how much I didn't like my Red Sea test kit I went out and got the Hanna checker.
Just tested today both to see how for I was off with the titration and digital.
Hanna: 6 dkh
Red Sea titration: 6.2
In your fourth picture is usually where I stop. Your last picture the yellow/orange is pretty vibrant. Never get mine that deep color. Figured I would share my experience
Sent from my iPhone using Aquarium Advice