Buy yourself a Hanna Instruments pHep®5 pH/Temperature Tester - HI98128. The probe is easily replaceable, it's waterproof, it floats, etc.... if you need to make EC measurements while mixing fertilizer then get the EC/pH/PPT tester. This brand is the best on the market, and I say this because I have used all others, and I use an EC and pH tester everyday in the field.