Which Are Useful?
There is a seemingly endless array of test kits for testing everything from ammonia levels to phosphate levels. Does one really need to buy them? The quick answer is no. It is quite possible to have a healthy tank without ever buying a single test kit. However, test kits are extremely useful at eliminating guesswork when something goes wrong (e.g., fish appear stressed or die). In the following, we describe the test kits that are most useful and the conditions under which they are useful.
Ammonia Test Kit
Get one. Ammonia test kits are cheap ($5-10) and will tell you whether your tank has elevated ammonia levels. This is useful in two circumstances. First, during the tank-cycling phase, regular testing for ammonia will tell you when the first phase of the nitrogen cycle has completed. Second, should you have unexplained fish deaths, testing for ammonia verifies that your biological filter is (or is not) working correctly. Note that even in an established tank, the biological filter can sometimes weaken or fail outright. Common causes include
* not cleaning the filter regularly (water can't flow through a clogged filter, where the nitrifying bacteria reside),
* naively adding fish medicines (antibiotics kill nitrifying bacteria (oops) as well as disease carrying ones),
* having too small a filter for the fish load, etc.
Be warned: if you have fish deaths and subsequently ask the net (or a fish store) for advice, the first question asked will be "What are your ammonia (and nitrite) levels?".
Ammonia levels are measured in ppm. At concentrations as low as .2-.5 ppm (for some fish), ammonia causes rapid death (consult the CYCLING SECTION for further details). Even at levels above 0.01-0.02 ppm, fish will be stressed. Common test kits don't register such low concentrations. Thus, test kits should NEVER detect ammonia in an established tank. If your test kit detects ANY ammonia, levels are too high and are stressing fish. Take corrective action immediately by changing water and identifying the source of the problem.
Warning: Amquel and other similar "ammonia-neutralizing" water additives are incompatible with most ammonia test kits. Water treated with Amquel will falsely test positive for ammonia, even when ammonia is not present. Test kits using the "Nessler" method are known to give false readings under such conditions.
Nitrite Test Kit
You might want to get one of these; nitrite kits are cheap ($5-10) and are useful in the same circumstances where an ammonia test is useful. The only time a nitrite kit provides information that an ammonia kit can't is while testing for completion of the second phase of the nitrogen cycle (see the CYCLING SECTION). As in the case for ammonia, if your test kits detects nitrite, your biological filter is not working adequately. Once a tank has cycled, nitrite kits are pretty much useless. (If the bio filter in an established tank isn't working, both ammonia and nitrite levels will be elevated.)
Nitrite is an order of magnitude less toxic than ammonia. Thus, one common saying about tank cycling is: "if your fish survive the ammonia spike, they'll probably survive the nitrite spike and the rest of the cycling process." However, even at levels above .5 ppm, fish become stressed. At 10-20 ppm, concentrations become lethal.
Nitrate Test Kit
Get this kit! Nitrate levels increase over time in established tanks as the end result of the nitrogen cycle. (The only exception to this rule is heavily-planted tanks and some reef tanks, which MAY be able to consume nitrogen faster than it is produced.) Because nitrates become toxic at high concentrations, they must be removed periodically (e.g., through regular water changes). Having a nitrate test kit helps you determine whether or not your water changes are removing nitrates quickly enough.
Nitrates become toxic to fish (and plants) at levels of 50-300 ppm, depending on the fish species. For fry, however, much lower concentrations become toxic.
Note: A nitrate test kit is only of limited value in determining whether the nitrogen cycle has completed. Most nitrate test kits actually convert nitrate to nitrite first, then test for the concentration of nitrite. That is, they actually measure the combined concentration of nitrite and nitrate. In an established tank, nitrite levels are essentially zero, and the kits do properly measure nitrate levels. While a tank is cycling, however, a nitrate kit can't tell you how much of the reading (if any) comes from nitrate rather than nitrite.
pH Test Kit
Get one; these kits are extremely cheap, so there is no excuse for not owning one. You will want to know the pH of your tap water so that you can select fish whose requirements meet your water conditions. In addition, you will periodically want to check your tank's pH so that you can be sure it stays stable and doesn't increase or decrease significantly over time.
In some cases, tank decorations (e.g., driftwood) or gravel (e.g., made of coral, shells or limestone) change the pH of your water. For example, tank items may slowly leach ions into your tank's water, raising the GH and KH (and pH). With driftwood, it is not uncommon to have the wood slowly leach tannins that lower the pH.
General Hardness (GH) Kit
You may want to get one of these, but having one is not critical. You don't need to know the exact hardness level. Knowing whether your water is ``soft'', ``very soft'', etc. is good enough. Your local fish store may be able to give you sufficient information. Alternatively, call your water utility (see the TAPWATER SECTION).
Carbonate Hardness (KH) Kit
This kit is not critical to have. By regularly monitoring the pH, you can figure out whether your KH is "high enough". That is, the KH should be high enough that your pH stays stable over time. If you have trouble keeping the pH stable, you may want to increase your tank's buffering capacity. Your local fish store may be able to give you sufficient information as to your KH value. Alternatively, call your water utility.
A KH kit is, however, indispensable to plant enthusiasts who use CO2 injection. It is also strongly recommended that you get one if you want to change the pH of your water, and it is a very useful diagnostic tool if you are experiencing pH stability problems.
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