Forum Thread: High Nitrate levels

You have a bio filter? Sounds like you need to add some bacteria to the tank to eat the plant waste.

"Where Do Nitrates Come From?

Nitrates are a by-product of nitrite conjugation during the latter stages of the nitrogen cycle, and will be present to some degree in all aquariums. Detritus, decaying plant material, dirty filters, over-feeding, and over-stocking the tank, all contribute to increased production of nitrates.

Water used to fill the aquarium often has nitrates in it. In the United States, drinking water may have nitrates as high as 40 ppm. Before adding water to your tank test, it for nitrates so you know if the levels are unusually high in your water source. If nitrates are above 10 ppm, you should consider other water sources that are free of nitrates."