Hey everyone,
This post is more directed at the newer hobbyist but applies to others as well. Test kits are one of the most important parts of an aquarium. Without knowing your water parameters you are operating your aquarium blind. This issue is largely the fault of the LFS not recommending kits at the beginning when a starter aquarium kit is purchased. Once a hobbyist has set up the aquarium, often test kits never come up. This is a huge problem and is the leading cause of failure among hobbyists. If you don't know what you water parameters are, you will likely never understand how your filter even operates on a biological level. without that knowledge, most hobbyists will fail, particularly with our tap water issues of low hardness.
Please, invest in a good set of test kits, you will save a lot of money over the long run. Sadly even aquarium publications don't stress this enough, I wrote into a number of magazines to profile this, no reply, surprise surprise.