I agree with moneyshot, and it is also my strong opinion that we should all have the little 2 ounce bottle of GH liquid pH indicator handy at all times to verify that indeed our pH calibration is correct. This is similar to the 'outside check' concept in analytical chemistry, where you check the accuracy of your calibration on a solution of known pH that is NOT one of the calibration standards- but in this case, you're using a different TOOL to check the SAME solution. Well, your res anyway.

If you own a pH meter you also need to have a set of calibration buffers, or you're wandering around in the dark.

Also, if you are using distilled water you have to use calmag.
stinkyattic Reviewed by stinkyattic on . hydro store messed up ph calibration HELP STINKY hey i was in my hydro store today saw the calibrating meter i asked did they do mine they told me to bring it in the said it was off so they calibrated now all it reads is very high like 11.4-16.0 ph dumped alot of ph down no change scared to feed my plants the open tomorrow at noon what to do just wait? Rating: 5