Water test kits are a must for every hobbyist, no matter what size aquarium and no matter what fish you keep. There are test kits on the market for almost every conceivable water parameter, so you may ask, do I need all of them? Most certainly not. Although having a test kit for every water parameter is certainly nice, it is by no means necessary. Here are the two most important test kits every hobbyist should have:
Ammonia Test Kit
An ammonia test kit is a necessity for every hobbyist and becomes especially useful when setting up a new aquarium. For those just starting out in the hobby, an ammonia test kit allows you to determine when a tank has finished cycling. In order to determine this, test the aquarium water every day until the test kit registers an ammonia level. At this point you have to wait for the bacteria population in the filter to grow and convert the ammonia into non-toxic compounds. Once the ammonia level reaches zero again, the aquarium has cycled. Wait for a further 48 hours to allow any nitrite to be converted into nitrate before adding the first fish.
Ammonia test kits are useful for another reason. By far one of the biggest reasons for disease and mortality in aquariums is ammonia. Therefore, if your fish begin to develop symptoms of disease or begin to die, test the aquarium water for ammonia. If the test kit registers anything besides an ammonia level of zero, there is a serious problem that has to be dealt with immediately. Finding the source of the problem, allows you to deal with the problem, therefore, an ammonia test kit is an absolute must have.
Nitrate Test Kit
Nitrate is an important water parameter to monitor, as it provides an indicator of the overall health of an aquarium. A nitrate level of anything more than 20ppm begins to adversely affect fish health in the long run. Therefore, regularly testing your aquarium water for nitrate can provide an indicator as to whether or not you should be carrying out more water changes, whether your filter needs cleaning or whether you can add more fish to the aquarium. Water changes and filter maintenance both reduce nitrate. On the other hand, a high nitrate level is a sign that the aquarium has too many fish in it.
Back to the issue of aquarium cycling; when the ammonia level reaches zero after spiking, you should then register an elevated nitrate level on your nitrate test kit. If you do not, then there is toxic nitrite in the aquarium. Usually nitrite is present for less than 48 hours. So if you do not register a nitrate level, wait a couple of days and test again. If you register an elevated nitrate level. The aquarium has cycled.
What about other test kits?
Once again, while all test kits have a use, there are some which are less useful than others in the long run. If you maintain a simple aquarium, with a focus on the fish, then water parameters such as pH, GH and KH should not vary much over time if regular water changes are carried out. Instead of purchasing these test kits, take a sample of your tap water to the local fish store and have the water tested for all the water parameters for a small fee. These parameters should be very similar to those in your aquariums if you carry out weekly partial water changes. However, if you maintain a heavily planted aquarium (see: Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise for the Home Aquarist) that requires the addition of nutrients or a marine aquarium, then there are several other test kits, besides the two above, that become vitally important.