I wouldn't reuse it. It's contaminated once you stick the probe in it. If you shop around you can find the calibration solution farely cheap. Petsolutions had a deal a while back. 79 cents a bottle. I stocked up then.
As long as you rinse the probe after its has been in the solution, you can reuse it at least several times. The ionic solutions of the calib solutions are very potent and will maintain their proper pH.