How To Test Your Aquarium Water Quality
Buy A Test Kit
Test kits can be found at your local pet store or purchased online. While some only test for one contaminant at a time (nitrates, ammonia, etc.), others test for them all at once. Many of these "master test kits" sell for $25-30. Some kits take 5 minutes to display results, others take up to 20. Some consist of vials and bottles, while others are just paper strips. It is important to read the description so you can make an informed decision about the product you are purchasing.
Or Visit Your Local Pet Store
Many pet stores offer to test your water for free or very cheap if you bring them a sample of your water. This is not ideal, however, because not only do you have to safely transport the water but will need to do so frequently. If you plan on maintaining a healthy aquarium you're water should be tested regularly and thus it is generally a better idea to buy a home kit.
Most kits will come with a vial and a suggested amount of aquarium water to begin with. Add the correct amount of water the the provided vial. There is usually a line on the vial to indicate this.
Kits will come with 1-3 bottles of solutions. Generally, you will add a specified amount of drops from Bottle 1 to the vial and shake. DO NOT shake with your finger over the opening, use the provided lid! Your finger can excrete contaminants and alter your results.
Continue with any other bottles that have been provided, following the instructions closely.
Wait for the specified amount of time to read results. This is important as results will continue to change until the time limit is reached and it stabilizes. Then simply compare the color of your aquarium water to the color card that comes with the kit. Find the closest match and that is your level!
Many kits that test for only one contaminant at a time will not have bottles and vials, but rather paper strips. If this is the case, submerge the strip in your aquarium water, swirl, wait, and read just like you would a master kit.
However, Always Read the Instructions...
This is a general guideline to provide aquarium owners with some basic knowledge on the process of testing water quality. Every product varies, however, and therefore you should always read the instructions for the specific kit that you have purchased.