ph meter and ph problems

My leaves have turned to a rust color so i assumed it was ph problem. I have been trimming the rust parts off. i bought a ph meter yesterday well 2. Both of them are giving me different readings at different times. I tested my ph last night with 1 of them and it said 5.9. So brought some lime. Today before I used the lime i tested with my other ph meter and it said 7.9 so I go back to the 1st one i used and it said 7.8. Just to experiment I mixed the lime with water and tested with both ph meters and it brought both meters down to the 5 range. I thought lime was supposed to bring ph up to alkaline area.
Does anyone have a comment about this.
Plus I put the meters into a bucket of cleaning acid and both shot straight up to 8.0 now I know this is acid, but these meters are doing the opposite of what I am expecting. When put in the lime they go down. Am I wrong I thought the lower the # the more acidic?

Are your meters tuned?

I had to tune mine, adjusting some little screws etc.

Did you calibrated the meter before you use it the first time?Did you let the probe soak in distilled water before calibration?Just asking but sometimes you can get a bad meter.But you said you have two meter and bove are readind the same.I would soak the meters probe in dw and recalibrate them.Test the water with bove meters and see what you have,and do this every 1/2 hour too see what your res is doing.Use the store brough PH up & down,it is buffered and will stabilize your ph easyer. well thats my two cents. PEACE