I'm currently using Petfran PH pen & UP PH meter & both serves me well. Petfran comes with a small pack of calibration liquid so need to purchase to do more calibration in future. As for me, i'm using the PH 7 & PH 4 calibration liquid which comes in a bottle form with the UP PH meter.
http://www.up-aqua.com/00-dm-page/00up_dm-ph-2-big.jpg
http://www.petfran.com/?page=pro_instruments
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