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i know it's an old question, but the search is dead, and i want to have a straight answer once and for all.

what are the conversion rates for the various aquarium substances?

Hi,
One dGH = 17.9 ppm.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

ok, noted.
keep them coming!
NO2, NO3, dKH, CO2, Fe, etc.

A milligram is one 1/1000 of a gram and a liter has 1000 grams, so a milligram per liter is one part per million!.

so 1ppm = 1 mg/L

but 1mg is mass, and ppm is number of particles ratios. they are completely different, afaik.

having 1/1000th part of the mass in NO3 isn't equal to having 1/1000th part of number, because NO3 and H2O have different masses per particle.
the molecular mass of NO3 is 62.
the molecular mass of H2O is 18.
therefore, you should divide mg/L in 62/18, in order to get ppm.
62/18=3+4/9
so a close measure will be (mg/L)/3.5, not mg/L.

are my calculations right? i can't consider myself sound at this hour, so help me out here :%)

Last edited by fry at 21-Oct-2004 17:37

No, think about it. if you have 5 mg of nitrate in one liter of water, thats 5 mg/liter, correct? So the mass of the nitrate is 5 mg. Well, the mass of one liter water is 1000 grams or 1,000,000 mg. Therefore you have 5 mg/ 1000000 mg or 5 parts per million (5 parts nitrate per million parts of water, the "part" being a gram in this case.)

I meant "the parts being milligrams in this case"

Just to clear the confusion up, 1 mg of WATER is exactly 1 mL, which is 1 ppm of a litre. . . substances with different densities will not share that trait. Actually, the SI units were standardized using these measurements.

Edit: Ok I guess I didn't exactly answer your question. . . following what I wrote above, you (technically)need to know the density of the substance in question to convert from ppm to mg/L and get a really accurate measurement. Most of the time, however, if you're just fiddling with anything you'd encounter in an aquarium, mg/L can be taken as equivalent to ppm, as you really don't need as accurate an answer and fluid densities will generally be close enough that you're not going to be way off. You probably wouldn't want to use that rule for saturation of gases like O2 or CO2 IMO.

Last edited by trystianity at 22-Oct-2004 13:21

first, there's no such thing as "one part of a mg". Grams are a measure of mass, not quantity.

what we need here is a way to convert mass into quantity. molecular mass does just that.
my calculations used the ratio between molecular masses to convert both mg of NO3 and mg of H2O into number of particles.

of course, molecular mass depends on the molecule in question.
NO2 -&gt; 46 (~1/2.5 conversion ratio)
CO2 -&gt; 44 (~1/2.5 conversion ratio)
Fe -&gt; 56 (it's Fe(3+), right?) (~3 conversion ratio)

now how do i calculate dKH?

Two people have told you that essentially 1 ppm = 1 mg/l, when dealing with water in the aquriums. If you already have it in your head to figure this out a different way (which is going to lead you into trouble), why did you bother to ask anyone about it? Since you obviously know what the conversion is anyway, or think you do..

i didn't think of it thoroughly at first.
my appologies for that.
but when i got the 1=1 conversion, it seemed weird, so on thought about it some more and got to some conclusions.
this conversion rate is surely wrong, because mass ratios are not quantity ratios.
mass is a linear function of quantity, but it isn't the same as quantity, meaning a linear correction is due.

yeah, it did get me back to highschool chemistry lessons
the things that those silent creatures revive in your brain...

Re-read my last post.

&lt;&lt;&lt; Currently studying chemistry at university.

can you elaborate on the part of density in the process?
afaik, as long as temperatures of the liquid are pretty close to 25C (in which 1L of water weighs 1kg), mg/L is a ratio of masses (mg/L=mg/kg(water)|temp=25C).

also, as far as i remember, the atomic mass unit is mass/atom. is it dependent on density by any way?

if i'm right about it, and i have the mass/molecule ratio, and mass/mass ratio, i can translate it into molecules/molecules ratio, and that's what ppm, isn't it?

where am i wrong about it? it starts being a bit confusing.

btw, why not add such calculator to the interactive section in this site?