I am running out of ph 7.01 buffer solution. I have 4.01 and 10.01. Can I use the 4 or the 10 to calibrate and still get accurate readings from 5 to 8?

Thank you sir. I should be good for a while then.

how often should you cal your meter? is there anything else you can use to cal your meter besides the solution?

I found that if you are using your pH pen often then rather than closing it up every time, pour some 4.01 cal fluid in a small cup that you pen can set in and just leave it in that when not in use. Make sure to rinse it off after each use with clean water and shake off any excess water before putting it in the 4.0 fluid. This will help it stay in calibration far longer than anything else. The most important thing though is to keep that bulb wet all the time as if it is allowed to dry out, it will not be able to calibrate properly anymore and you will have to get another probe or whole new pen.

i use cheap yellow pen....leave it in the 7 o bag all the time.....have another bag to calibrate...like 4 bucks worth max...i use the second bag over and over to check....seems to keep me good for a year..
check the pen all the time..cant check too much...