Can This Be Used To Read the pH When Using Hydro??

if you're growing with recirculating drip hydro will this work to get a read on the ph? if not why would it not?

http://www.amazon.com/Luster-Leaf-Mini-pH-Tester/dp/B001BBFKQG/ref=pd_bbs_5?ie=UTF8&s=hi&qid=1235003644&sr=8-5

negatory...thoose things done even work well for soil.