Water testing can be a mystery to newer keepers. Though it's only occasionally needed in established freshwater, accurate water testing is vital in both marine and marine reef tanks. In this post I'll explain the three most common methods of water testing, with their pluses and minuses.

The most common water testing kit most new and some not so new keepers purchase are test strips. A strip, say for Ammonia, is dunked in aquarium water, and the strip will turn to a color. The color is matched to a chart, giving the user an approximate reading.

The Pluses: Very inexpensive and commonly available. Very simple to use.
The Minuses: Less and less accurate as time goes by due to humidity in the air. Readings are always suspect.

More accurate are drip-based test kits, which are what most strip users graduate to when they realize strips are near useless. Regents, which are dyes and solutions available for a dazzling number of water parameters, are dripped into vials containing small samples of aquarium water. Each different test requires a set number of drips.

The resulting color in a vial is matched to a chart for the reading. Hobby level regents are relatively accurate, but miles more accurate than strips. Laboratory-grade regents are more expensive, but are very accurate. Coupled with an electronic device called a colormeter, regents are dripped as above, but inserted into the device for a truly accurate reading.

The Pluses: Far more accurate than strips, simple to use. Commonly available.
The Minuses: More expensive than the strips, can be confusing matching samples to charts. Regents will expire over time, usually within a few months. Colormeters are very expensive.

The most accurate piece of equipment you can buy are electronic meters.

Models can be for a single parameter, like pH, and better models come with a probe that's dipped for a set time in an aquarium water sample. Some more expensive meters test multiple parameters, some with a single probe, some with two or more probes.

Electronic meters are without doubt, the most accurate of testing methods. For example, my pH meter reads to the hundredth place, like pH 7.26. The margin of error is one-one thousandth, meaning the water can be pH 7.25 or 7.27. If you want to know how much dissolved Oxygen is in your water, an electronic meter will tell you, in mg/l. If you want to know how much is used by the life in your tank during a 24 hour period, a meter will tell you that, too. Testing Ammonia in a new tank? A meter will tell you, to the thousandth place.

Meters are available that will test all the common freshwater and marine parameters. If you want to know a parameter, there's probably an electronic meter for it.

The Pluses: Highly accurate. If you want to know an exact reading, the only way to be sure. Properly maintained, can be used for many years. Simple to use.
The Minuses: Expensive. You can expect to pay around 80 dollars US for a good pH meter. Other meters can be hundreds, like 250 for a Calcium meter, or thousands, for top-grade multiple meters and some top of the line single meters.
Meters must be regularly calibrated for continued accuracy. Probes eventually must be replaced.

These are the three testing methods available to the aquarium keepers. Each have their pluses and minuses. The vast majority of hobbyists use regent-based test kits, as they know they are much more accurate than strips, and are only moderately expensive. Electronic meters are the creme de la creme of accurate testing, and it's only the price that restricts their use.

I use both lab-grade regents with colormeter, and electronic meters. I use both methods to verify each other, and for my peace of mind and thus the benefit of the fishes. I enjoy testing, and do so weekly with my tanks, and chart the results over time so I can spot trends.