Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Here are the tests that are most common, and why they are used:
Ammonia: Toxic to livestock. Important to monitor while you are cycling, and a very good thing to check when something goes wrong.
Nitrite: Toxic to livestock. Important to monitor while you are cycling, and a very good thing to check when something goes wrong.
Nitrate: The end result of the nitrogen cycle in the aquariums. If this was a non-planted set up the nitrate would tell you when to do water changes. In a planted tank it tells you if you are fertilizing the plants enough. Low tech often means fish food is the N source, and plants are using it slower, so you may still have to do water changes if the NO3 gets too high.
pH: A general check on whether overall things are going OK. As long as it is stable that is fine. One way of monitoring the CO2 is to monitor the pH. When the pH is varying in a set pattern it means the CO2 equipment is running right. If the pH is low and there is ammonia present in the water then that ammonia is more likely to be in the form of ammonium, and is not so toxic. As the pH rises more of the ammonia is present as ammonia which is toxic.
GH: General Hardness is a test for calcium and magnesium. These minerals are important for fish and plants. Many fish prefer water that has a certain range of GH. I would count this as a very important test.
KH: Carbonate Hardness is a test for carbonates. Carbonates are a buffer that stabilizes the pH. When carbonates are high the pH is usually high. When carbonates are low the pH may vary more easily, and other chemicals in the water may control the pH. This can be just fine, especially for soft water fish.
TDS: Total Dissolved Solids tells you overall how much 'stuff' is in the water. Many people with heavily planted tanks or shrimp tanks rely on the TDS to tell them when to do water changes. Any salts or minerals added to the tank can make the TDS rise, and as the plants remove the fertilizers the TDS drops.
Aquarium Plant Fertilizer tests are generally not used much, but if there is any suggestion that there might be a plant deficiency it might be a good idea to get one or more of these. There are always questions about reliability.
Phosphate: Also comes from fish food, so when the nitrate tests are in the right range I assume the phosphate is, too. It sure is NOT actually linked to nitrate, just that the main source in my tanks is the same material (fish food). If I need to dose nitrate, I also dose phosphate.
Potassium: A very important plant fertilizer, but I just dose it without testing. There is not any other source in my tanks, so before the plants show potassium deficiency, I dose.
Iron: Perhaps the one test of this group that might be worth getting. Iron is one ingredient in trace mineral blends. Often trace minerals are dosed by keeping the iron in the right range.
Calcium: When testing the GH you are getting a combined reading for Ca and Mg. If there is any question about a problem with the GH, then a Ca test and a little math can tell you how much of each you have, and if you need to dose one or the other.
Salt: I have this test for my brackish water tank, and I have tested tanks that I am treating for Ich, and I test water that comes from the fish store with fish, so I can make the quarantine tank the right water chemistry. I sure do not recommend this test. You can simply ask at the store if they are running their tanks with salt and how much.