need help with my ph pen please

hey guys,i really need some help here please.my ph pen is acting really weird.when i take my reading it keeps jumping from4.9-6.0 and back down.the batteries are good so i was thinking that it may need to be re-calabrated.plus when i do my readings on one side of the res,then the other side of the res(10 gal res)its totally different.one side will be 5.5 and the other side will be like 6.8 or some thing crazy like that.i also just got a new digital ballast and ive been told that the higher freqency of the ballast will mess with ph/tds pens,is there any truth to this.any help with this will be great,thanks

you shoul have a calibration mode on your pen, and get some ph7calibration fluid . try that and see if it reads correctly..

thats what i was thinking,just re calabrate it and go from there.thanks for the help.does it matter wich re cal solution i use, they have the 4.01 and 7.01.

shouldnt make no difference mate, i personally use 7... if that pen is digital the probe needs to be kept moist with the fluid to when not in use..