Does your test kit test higher than 8.5 or is that the last color? If last
color, you really don't know how high your pH is. Personally I really like
the Nutrafin wide range tester that goes from 4.5-9.5. ~ jan

Alex wrote Looking at the colour of my test kit, the PH is 8.5. The high end
I know, but I was under the impression comets could live with that. Am I correct?

(Do you know where your water quality is?)