WHAT EVERY AQUARIST AND POND KEEPER SHOULD KNOW ABOUT NITRATE TEST KITS...

KPD-63
Understanding the nitrate water quality test kit reading is complex, and has many users confused, including experts. It is worth the time to review the following information to help you have a better understanding of what nitrate test kits and their readings are all about. Nitrate is in only one molecular form... NO 3 - and is relatively nontoxic to aquatic life, including fishes. However, monitoring nitrate levels is a very good way to keep track of other toxic elements that may accumulate at a rate similar to nitrate and which are much more difficult to measure.

While there is only one form of nitrate, there are two kinds of nitrate test kit readings -- one for the nitrate ion and the other for nitrate/nitrogen (the amount of nitrogen in the total nitrate reading). Some pond and aquarium test kits read as nitrate ion, some read as nitrate/nitrogen, and the rest don't explain which way they read. Older Kordon Nitrate Test Kits read in units of nitrate ion, and not as nitrate/nitrogen. The latest generation of Kordon's nitrate tests kits read both the nitrate as ion and as nitrogen. Also note that the pH (acidity/alkalinity) of the water does not affect the nitrate in the water or test kit readings. However, declining pH (increased Acidity) is often a reliable indicator of deteriorating water conditions.

NOTE: The reason for doing a nitrate test of the water is mainly not because of its toxicity to fishes or other aquatic life, but to get an indications of other toxic organic compounds that increase in the water at about the same rate as the nitrates. The simplest way to measure these toxicants is by measuring nitrate.

WHAT IS THE DIFFERENCE BETWEEN THE TEST KIT READINGS OF NITRATE ION AND NITRATE AS NITROGEN?
Many aquarists and pond keepers are perplexed by the use of the terms nitrate ion and nitrate/nitrogen (or nitrate as nitrogen), and do not know what the difference is between the two. The differences between the terms are in how the chemical composition of the same nitrate molecule is being measured, which can be in two different ways, giving two different readings, each of which is correct. If you have a nitrate/nitrogen reading, it can be converted to the ionic nitrate reading by multiplying it by 4.4. If you have an ionic nitrate reading, it can be converted to the nitrogen reading by dividing it by 4.4. For example, if the nitrate ion concentration is 50.0 ppm: 50.0 divided by 4.4 equals11.4. The reading would be 11.4 ppm as nitrate/nitrogen. The conversion factor of 4.4 is based upon the atomic weight proportions of the nitrogen and oxygen in nitrate (4.4 weight units of nitrate contain 1.0 weight units of nitrogen).

If the nitrate is measured as the total molecular weight of the molecules of the nitrate compounds in the water, which will be NO 3 -, the total amount of combined nitrogen and oxygen atoms in the molecule are being measured as nitrate ion. If only the nitrogen atoms contained in the complete nitrate molecules are being measured and the measurement for the hydrogen atoms is left out, this reading is for nitrate as nitrogen (N).

Most information in the aquarium hobby refers to nitrate as the nitrate ion, so when you see the reference to nitrate as 20, for example, this usually means in aquarium publications the total molecular weight for all of the nitrate molecules. The number 20 means that the total weight is in ppm (parts per million), or mg/L (milligrams per liter, a very close counterpart having essentially the same measurement). When the information provided does not indicate whether it is as nitrate ion or nitrate/nitrogen, there indeed can be confusion as to which is being measured. However, when you remember that the two readings are different by 4.4x, it may be possible to know to which of the two types it is referring.

Why are there two different ways to refer to measuring the amount of nitrate in the water? In scientific measurements of water quality in lakes, streams and oceans, the amount of nitrogen in water, whatever the form, is an important measurement. Therefore, the reading for nitrate as nitrogen is widely used in the scientific literature. In biological laboratory research on living aquatic animals, the amount of total ionic nitrate present is more important to know, as it has a more direct impact on the animals. Therefore, in this type of research, and in much of aquarium and ornamental pond keeping, it has been more important to measure nitrate as nitrate ion. But keep in mind that both readings are correct, and either reading can be directly acquired by multiplying or dividing by 4.4 respectively.

WHERE DOES THE NITRATE COME FROM?
In aquarium and pond keeping nitrate mostly comes from the conversion of nitrite to nitrate by nitrifying bacteria in the water. Over time (usually less than 4 weeks in tropical aquaria; less than 10 weeks in outdoor temperate water ponds) the amount of nitrate in the water will start to increase. Even though nitrate is not nearly as toxic to aquatic animals as ammonia or nitrite, it is very important to measure because it is a good indicator of the parallel build up in the water of organic compounds that are likely to be toxic to fishes and other aquatic life. A nitrate test is not done to determine just the nitrate level, but to give an indication of the amount of other toxic elements in the water that otherwise cannot be measured. Therefore, constant monitoring of aquariums and ponds (set up for three weeks or more) by use of nitrate water quality test kits is essential.

WHEN THE NITRATE READINGS ARE MADE, WHAT DO THEY MEAN?
This question is often asked by aquarists and pond keepers wanting to know what the significance of their readings really are. There is usually a very wide tolerance by freshwater animals and fishes to the organics present in the water as indicated by the nitrate test; most kinds tolerate levels of 100 ppm and greater, as shown by nitrate ion concentrations. However, there are exceptions, such as in electric fishes (elephant-nosed fishes, knife-fishes, stingrays, catfishes, etc.), for which readings should not exceed 25 ppm. There is a much narrower tolerance by saltwater fishes and invertebrates, and their readings are best kept below 25 ppm as nitrate ion. For specific aquatic animals check the technical aquaristic literature for their tolerance to nitrate. The simplest way to lower nitrate in the aquarium and pond is by partial or total water changes. Plants also utilize nitrates as a food source and will remove some from the aquarium and pond water. This is why high nitrate levels often result in heavy algae growth.

In general: aquatic animals (including fishes) that come from a clean water environment, such as from highland streams, swift-moving water conditions, open ocean, coral reefs, etc., have a low tolerance for nitrate ion readings above 25 ppm. The same is true for sick fishes. Aquatic animals (including fishes) from lowland streams, slow-moving water, swamps, mangroves, etc., have a higher tolerance for nitrate readings above 50 ppm total nitrate. Most marine animals have a lesser tolerance for organics in the water than freshwater animals. This includes many crustaceans (crabs, shrimp, lobsters) that cannot stand higher levels of nitrate. To keep on the safe side for general aquarium and pond conditions do water changes as soon as you see 25 ppm or more nitrate ion in salt water and 75 ppm for fresh water. What about using products that remove nitrate? Other than for marine fishes and certain exceptional freshwater fishes, there is limited practical use for these products in aquarium and pond keeping.