I've just lost all faith in my Chinese ph stick. calibration drifted a full point over night and when re calibrated it didn't give me readings close to what i was expecting and they take forever to give a reading. Spend the money get a good one. They only cost the same as a couple of test kitsI got a 5 quid ebay job from China, seems to work okay, probably not as accurate Hanna but it does the job for me. I just have to re calibrate it every so often but it's never that far off the buffer solution pH.
I've just lost all faith in my Chinese ph stick. calibration drifted a full point over night and when re calibrated it didn't give me readings close to what i was expecting and they take forever to give a reading. Spend the money get a good one. They only cost the same as a couple of test kits
This is the one i'm about to buy
http://www.digital-meters.com/chemical-analysis-c2/orp-meters-c27
I went to reclibrated mine this morning for the first time in like 3 months and it was 0.1 out on the 4.0 solution and bang on 6.9 on the 6.89 solution. I didn't bother touching it. Not like I take very good care of it anyways, I might rinse the thing under a tap after dunking it the tank if I remember to. I just don't see the point of spending £50+ on something for me isn't that important, hitting that 30ppm isn't that important for me since I'm on low lighting. As you know Andy the water around here aiming for the 1ph swing doesn't really mean anything and my nominal pH at the begining of the week is completely different by the end of the week.
I use the pH pen as a rough guide to see what the CO2 is doing in my main tank is at and to make sure my invert nano tank doesn't drop below a neutral pH.