Nitrate in Koi Pond

Nitrate is produced by aerobic oxidation of nitrite by chemoautotrophic bacteria. The nitrifying bacteria oxidize the nitrite to nitrate to produce energy, unlike photosyntesis, this can occur even in the dark, as long as oxygen is present.

Nitrate is relative nontoxic, and koi can survive at levels up to  200 mg/L, but do the best if nitrate is kept below 20 mg/L.  The accumulation of nitrate will reduce the buffering capacity (alkalinity) of the water over time, wich will allow the pH to decrease (become acidic). Nitrate acts as fertilizer for algae, and high levels will stimulate alga blooms. Also high nitrate levels will interfere with salicylate method  ammonia testing. Keep the level low by periodic water changes and removal of dead plant material from pond.

Some water test kits give the results of nitrate test as nitrate-nitrogen, wich is the measure of only the nitrogen component of the nitrate molecule. To obtain the total nitrate level with these test kits, multiply the value of nitrate-nitrogen (in mg/L, or PPM) by 4.4 to equal the total nitrate level.