Milligrams per Liter ( mg/L) versus

[hammy]

read this from a book and thought it might interest some of you.

Concentrations of trace elements and unwanted wastes are reported in ppm. if a 'part' in ppm refers to 1 gram, then ppm will refer to gram per million grams. as long as the ' parts ' are identical units , then using 'ppm' is accurate.

the term mg/L is a measure of mixed king of parts. milligrams ( weight )and Liter ( volume). It is inaccurate to refer as 1mg/L as 1 ppm.

Here's why.

One Liter of natural sea water has a mass of approximately 1.025 Kg/L.

Pure water at 4 degree celcius has a density of 1.0000 or 1 Kg/L.

if you measure nitrite in seawater from a marine aquarium and the value on the test kit kit is '1.00' ( either as nitrite ion 0r nitrite-nitrogen) , what the test report is 1.00 mg/L. This means that each liter or water contains 1.00mg of the substance.

This same value, 1.00mg/L if reported in ppm, would actually be 0.9756ppm. that is because 1.00mg/L is equavalent to 1 mg per(1 liter X 1.025 Kg/L); or 1 mg per 1.025 Kg; or 0.98ppm

The difference is only 2.5 %.but it is a real difference . better quality test kits usually report results in mg/L and not in ppm.

--Marine Reef Aquarium Handbook by Dr. Robert J. Goldstein

[May&Bruce]

yep.....for approximate purposes its ok to assume that 1 ppm = 1mg/L for seawater, but if more accuracy is required then you need to decide which units to work in. The better books and better test kits seem to refer to mg/L, which I also prefer to use.