Nitrates

By Gary V. Deutschmann, Sr.

The unscientific controversy on nitrates, expounded by many ill-informed, yet popular authors, columnists, and test kit manufacturers, continues to plague aquarists both mentally and financially worldwide.

I would like to dispell most of those negative myths about nitrates, and the the so-called "nitrate poisoning" touted by many aquarium shops as the cause of death of your prized animals.

The evaluation of various test kits (and the reliability of their readings) has been covered exhaustively elsewhere, and will not be reiterated here. Suffice it to say that the NO3-N scale, with levels expressed in mg/l, is the most scientifically accepted conversion scale and used in this documentation. For our purposes, the units of mg/l are equivalent to ppm.

I will start by stating one simple fact: nitrates are not particularly toxic! However, testing for nitrates is one of the most useful indicators of the quality of your aquarium water. Nitrates, along with pH, can be used to determine when water changes are actually necessary.

The use of artificial denitrification devices to keep nitrate levels low can give the aquarist a false sense of security. No longer will a simple low cost nitrate test indicate a drop in water quality, and the presence of other potentially harmful compounds, indicating the need to perform a water change.

Lower nitrate levels (than those indicated below) are naturally preferred and should be maintained as low as possible when feasible. I might point out that most experienced public aquaria curators have mutually agreed that 50mg/l should be considered the upper limit, even while the aquaria under their direction, usually through governmental restrictions on discharging saltwater, have risen to well above 100mg/l and one particular public aquarium drifted above the 500mg/l reading for a short time. In our smaller home aquaria, the following scale should be considered the upper limits.

• 40mg/l Marine Aquaria holding non-reef or hardy fishes.
  
• 20mg/l Marine Aquaria holding delicate reef fishes.
  
• 10mg/l Reef Aquaria holding invertebrates, including delicate Acropora.
  

I hear you gasping at how high these levels are, so without consuming too much valuable space, suffice it to say that scientific research conducted by Mote Marine Laboratory and published in the "Journal of the World Aquaculture Society", using the LC50 toxicity test, showed a common reef fish, the beau gregory, reached 50% mortality at 2,400mg/l the high and a planehead filefish, reached 50% mortality at 500mg/l the low for marine fishes. A practical range for Invertebrates, including anemones and corals, has been determined to be between 20 and 40mg/l in public aquaria. While the hard hermatypic corals and Acropora, in a home aquaria setting can only withstand a high of 10mg/l for an extended period, such extended period being a month shy of 4 years.

I am often asked, "So, if what you say is true, when do we perform water changes?" I prefer to see that normal 5% water changes are carried out on a routine basis. However, if you monitor your tank closely and find a drop in pH to 8.0 or less, and nitrate is high (40/20/10mg/l respectively - see above) it is definitely time to perform a water change.

In closing, I would like to state that good water quality is essential to maintaining a healthy and thriving aquarium. Testing nitrates is one good way to keep abreast of the potentially harmful compounds that the home aquarist does not have the facilities or equipment to monitor.

Written exclusively for RTO Features by Gary V. Deutschmann, Sr.

HTML by RTO. Copyright 1996.