I also experience testing to the minimum on the liquid API. Bought one off of ebay for <$12 shipped. 3 tanks tested in the low to high 4's (several members here could not believe my fishes, shrimp survived - I did have some clown loaches dying). Was really surprised, but after several calibration with 4 & 7 buffer soln, was confident of the meter. Also, I had one tank that was reading around 6.6 on liquid and meter read 6.7.
I wanted to get my tanks back to around 6.2, so finally accomplished that with crushed corals. And meter still tested fine against the API liquid once I got back into the 6's.
It's not a high end pH meter, but it did the job. This meter was shipped from the US.