need help with my ph pen

whats up riu,i have this in another thread but no hits so i thought i would try here.my ph pen is acting really weird,it keeps jumping from 5.0 - 6.0 and wont stabalize.and when i take a reading from one side of the tank and the other i get way different readings and its only a 10 gal res filled with 6 gallons.i was thinking it needs to be calabrated or it is my new didital ballast.ive been told that the higher frequency of digital ballasts will mess with ph/tds pens but it didnt do it the first few days of the new ballast so i dont think thats it,any help with this would be great.

mine does it occasionally i have a cheap one. i turn it off and back on and check the calibration. some days i just go back to the drops to check ph it if it doesnt want to work. sorry no fix for you really.