JackHerer, the calibration solutions are available on line or at hydro shops. You should calibrate at least every 6 months, 3 is more safe. Also do not use old solutions as they can be wrong (found out the hard way). Grab the farthest one back on the shelves, not the older ones in the front that they want you to buy.
Everyone, I've had pretty good luck with my Control Wizard brand stuff. Inexpensive, durable, and accurate (I think). I want to buy a real nice expensive one some day soon, but my separate PPM and PH meters have done me real good so far. Also low batteries give false readings. I found that out the hard way as well. The batteries that came in my PPM pen were almost dead. I took it back and they gladly replaced them. And those batteries can cost almost as much as a new pen.