I did a little googling and found this, but it is for people with aquariums. Nitrite is the result of the metabolism of ammonia by Nitrosomonas bacteria, which oxidize ammonia (NH3) and convert it into nitrite (NO2). This is a part of the nitrogen cycle, which is discussed in great detail in our articles. Nitrobacter species of bacteria take the process one step further and further oxidize the nitrites into Nitrates (NO3). Nitrite is fairly toxic and in a well-balanced, aged aquarium will always test at zero. It is unavoidable to have nitrite in a tank that is new, where the nitrogen cycle is not complete because there are not yet enough bacteria to treat ammonia and nitrite. As the bacteria populations rise, ammonia and nitrite levels both fall to zero. Provided you don’t over-stock the tank or add fish too quickly, you will see little fluctutation in these levels. Nitrates are always present in most aquariums. They do not get removed through normal biological filtration. They are removed by algae which consumes them as food, by anaerobic de-nitrifying bacteria which occurr naturally inside of live rock, and by water changes (the most common way of reducing nitrates). Invertebrates cannot tolerate much nitrate, so it is best to keep the levels below 20ppm for reef tanks. Fish can tolerate a great deal more than invertebrates, but we would not advise letting nitrates exceed 120ppm in a marine fish tank. Does that help?