Submersible pump making ph pen malfunction?

I'm setting up my first reservoir for a drip system.. I have a small submersible pump in my res for keeping things agitated, when I check the ph with the pump inside the res and running I get funky reading of 0 to 3.0, when I turn the pump off I get a reading of about 5.0, when I take the pump out of the res I get a reading of 7.8 which seems correct there is only tap water in my res at the moment.

Is this normal? are you able to test the ph of your res with a submersible pump running? is my ph pen broken?

I came to the conclusion it's my PH meter on it's way out, the ph meter was later giving funny readings in a cup of water and I observed the screen glitching out a few times.

Strange that the submersible pump was making it glitch out even harder.

I wouldn't rule out the meter just yet.
I'm getting the same thing happening to me. I'm using the older tri-meters. When I switch the prob from my new one to the one that's being funky like you discribed, it would still give the same results.
If I shake the pen in the nutrient solution a bit it seems to start giving better results. I have not deturmined the problem for myself. I am running a circulation pump 24/7 that seems to through off the readings a bit if the pump is directly beside the prob.
I keep it on the other side of the reservoir but it still gets funky sometimes, but yet it's completly fine in a glass of plain water.
I also would like to try putting the meters on there own circuit with nothing else plunged into it.
For example: the circulation pump, or any ballasts.
Does your meter have a ground wire? Mine do not and that to me seems odd.

I put in more powerful air pumps/stones and I am finding it harder to check ph. The bubbles are a slightly different ph it seems so I put it into the calm.

A little shake in the water helps mine also. I think it needs calibrated because it bounces around before finding the ph and starts farther away from the true ph's number.

Does yours have a calibration option? Don't get rid of it if it does.

Growstores sell calibration solution and some stores do it for a minor fee. I need to get to the growstore myself it definately makes the daily work longer and aggitating.

I have been buying these cheap $10-20 PH meters off amazon, http://www.amazon.com/gp/product/B00FJFEB2O?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s01

I also buy the calibration solution from general hydroponics, I use my meter pretty much daily so I always keep it clean, calibrated and I keep it stored with the tip in a glass of clean distilled water, I know they make a storage solution but so far this has been working for me, My cheap meter stays pretty well calibrated if I take good care of it, I have gone through about 3 meters in 2 years, I claim responsibility for the meter deaths, I either let them dry out for long periods of time or dropped them pretty hard.

I have a new cheap meter on the way should be here today, Hopefully it does not do the same thing.

I'm thinking of buying an Oakton or Bluelab PH meter.. But I hear its pretty much the same thing with their meters and they cost a lot more. Also been looking at a Bluelab guardian to make things easier.