The Hanna Checker 1 pocket sized pH meter is adequate for aquarium use and is reasonably priced $20-$30 on ebay. The probe lasts for about a year and can be replaced for about $18.

I work in a calibration laboratory and have access to good reference solutions. The meter worked well, up until the probe finally died (the point to where I could nolonger adjust the 2 point calibration to match the buffer solution values).

To be fair I did not use this probe continuously, only periodically to check my pH to make sure it had not changed drasticaly from where I thought it should be, and I calibrated it before every use. I also stored it dry with just the rubber cap over the sensor, and didn't use the recomended storage solution. I went several months of use before I had to make any adjustment after the first couple of calibrations. Durring this time it consistantly read correctly within 0.05 pH between 7.0 and 10.0 even though Hanna specs it at an accuracy of 0.2 pH. It has a resolution of 0.01 pH.

I trusted the reading on this meter more than any of the hobbiest liquid test kits.

My opinion is that even though it is not nearly as good as a good laboratory pH meter, it's great for home use, however I would suggest calibrating it at least once a month to maintain the accuracy I managed to.