Why do I need to check the water 'alkalinity' or 'hardness' in my aquarium?
Alkalinity or water hardness which are sometimes the same thing, for this discussion we'll call it the same thing, are really important to keeping pH stable. They are basically measuring the amount of mineral content or trace elements that are in the water. Those trace elements act as a buffer of your pH again, fighting the bad guys which is acidic amonia nitrate, nitrite and some other things like phosphate that we haven't talked about, kind of fighting them from driving your pH down. They're the stabilizers of the pH, which is critical to any type of system be it fresh water or salt water. When you're testing for alkalinity, KH or DKH, alkalinity or water hardness there are simple kits like there are for almost anything you're going to test for that you can get in any reputable aquarium store. They're very simple and easy to read. They will tell you basically what you're levels are and what you want them to be. It's not nearly as critical typically in fresh water as in salt water and again when you're talking the salt water fish only versus saltwater invert coral and fish they have different requirements as well, so you have to kind of know specifically what you're testing for based on what you have. But they are very easy to use, the test kits are very easy to use and they are very easy to read.
