Difference of pH between nutrient medium and hydroponic medium

I tested the pH of my nutrient water with a lab quality pH meter to be around 6.7-6.8. However, when I put my crappy $12 soil pH meter into the coir, I get a reading between 7-8 (closer to 8 I guess, but it's hard to tell). Is that right? Can there be pH differences between the medium and nutrient water, and if so, how does it happen, and what can I do?

yes, buy a ph lower'r... you might need to flush first