Most calcium reactors rely on some type of pH controller in order to regulate the amount of CO2 that is being used, thereby changing the amount of calcium carbonate media is being dissolved. These controllees rely on pH probes, obviously, and it is important to maintain these probes in the best shape possible. This requires calibrating and replacing the probes as needed, but nobidy ever knows when to do these two steps. Are they performed at certain intervals? When the probe fails? Well, the answer is both actually. To check the probe, simply take it out of the reactor, clean it with purified water, and soak it in a buffer, preferably the 7 pH buffer. If the reading is within 5-10% of the expected value, you should be in good shape. Anything outside is that window means your probe needs some attention. And even though we geared this article towards calcium reactors, you can apply the same tips to any pH probes really, whether standalone or as part of a controller package.