I use a Pinpoint pH meter to check the pH in the tank and I use a pH probe from my controller for the calcium reactor. The Pinpoint pH monitor seems to work well, I haven't had any problems with it. There have been a couple threads on RC about the unreliability of the Pinpoint calcium monitor (in terms of the accuracy of the readings), so that one might not be worth the money. Not to mention that they run around $250, which will buy a lot of test kits and still leave plenty left over for beer money.