TETRA - etratest Nitrate and Nitrite Nitrate is the end product of biological filtration and the result of decomposition of nitrite. It can also be present in tap water supplies, especially in areas of high fertilizer run-off. Although virtually non-toxic to fish, nitrate is a key algae nutrient and high concentrations can harm your fish. Nitrate testing is also an indicator of general water quality and filter function; as biological filtration converts ammonia to nitrite and finally to nitrate, other important chemical changes take place in the aquarium. These changes can include the loss of alkalinity (buffering capacity) or the accumulation of phosphate - thus nitrate testing can indicate possible imbalances in other areas without directly testing each one. This kit is suitable for freshwater (including outdoor ponds), brackish, and saltwater systems. Price for Each Test Kit. Nitrate and Nitrite are two seperate test kits. If you need both order Qty 2 and lot more Tetra Products.