Do you have any idea how many dissolved minerals there are in your water? Neither did I when I got started with my first fish tank. Luckily I lived in an area where the tap water was pretty good for my fish, but learning more about the chemistry of hard and soft water has sure helped me over the years.

First thing to know is, most tap water is "hard water", which has lots of calcium and magnesium dissolved into it. This is good for your tank and your fish!

Hardness is measured in "parts per million" of calcium carbonate, and the "general hardness" of the calcium (gH). "Soft water" has under 135 ppm and 4 to 8 gH, while "hard water" has more than 200 ppm and 12 to 20 gH. You'll want to find a test that helps you measure the ppm in your tank: a "general hardness kit" measures gH, although you can often get a good answer with a phone call to your water utility, whose job it is to keep track of hardness.

There's a separate "carbonate hardness kit" that will measure the amount of calcium carbonate (kH) in the water. This usually involves a process called "titration". You just add drops of a chemical to a water sample, and the number of drops required to change the color of the water-plus-chemical mixture tells you the kH level. There are also some kits with pre-treated paper strips you can just dip in the water, but these only tell you a general range.

The only time you really need to worry is if you're water's very soft, because there's less of that calcium carbonate to buffer the normal ups and downs in your tank's pH balance. Without that buffer, your pH can fall very far, very fast, which will at least make your fish and creatures sick, if it doesn't kill them outright, and if it happens when you're not at home or not paying attention, the effects can be devastating.

So what do you do if your water's too hard? There's several ways to it a little softer. Boiling the water is the simplest, but most time consuming. A peat moss filter or a reverse osmosis system are probably the most popular techniques. You can also find "ion exchange resins" that will help.

And if the water's too soft? That's even simpler - just try filtering it through crushed coral or dolomite. The minerals will start to leach into the water, so just keep filtering and testing and you'll find you have properly "crunchy" water in no time.