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Nitrate Mass Balance

I'm new here.  I'm a chemical engineer and have worked with a lot of water treatment projects.  I'm a bit skeptical of some of what I read on the internet of aquariums, but enjoy reading about the biology of a planted tank.  The problem with biology is the lack of quantitative data.  I uptake of Nitrate by plants is over estimated.

Nitrate contains about 22.6% nitrogen.  A 100 gallon tank with 30 mg/L nitrate contains  2.7 grams of nitrogen.

Now a dry plant contains 10% N and a wet plant contains 98.5% water.  So for the plants to consume 2.7 grams Nitrogen they must grow 10 times that or 27 grams (dry).  With the water this is 27/1.5%= 1800 grams.  Remember Nitrogen is an element it can't be broken down (short of nuclear fission!) so what comes out= what goes in  minus what stays in.

In other words for plants to clean a tank with 30ppm NO3 to 0 ppm NO3 the plants would need to grow 1800 grams or about 4 POUNDS WET.  If I'm wrong on these calculations it would be the estimates for % H2O in an aquatic plant and the % N in an aquatic plant but I shouldn't be off by much.

Dave Kysar    

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