How accurate will a soil ph test kit measure reservoir ph in hydro?

My ph pen gave up on me and all i have available is a rapitest soil test kit. The PH was reading high (7.1) with the pen and it seems the soil test kit is aswell. I know the pen needs calibration since i was unaware of handling instructions, but what are the chances the soil test is also giving a bad reading?

If its litmus paper, sure why not. Ph is Ph.
if your readings are all whacked out you know it doesn't work.

If they both read high, but close to each other, I think they are probably correct for the most part.

Thanks...added ph down and the soil test kit picked up the change. The ph pen read a higher ph!!