µmols to ppm help...

[mcarroll]

I'm reading too many things giving me nitrate and phosphate concentrations in µmols but I speak ppms.

I'm sure since I learned to read ppm's in the hobby that it's wrong or at least antiquated. ;)

Can someone tell me how to convert ppm's of NO3 and PO4 to µmols?

I have only gathered enough to know that it's not a straightforward conversion factor kind of thing.

Thanks for any answers or pointers!!


P.S. If you can also explain, if both units are usable for expressing concentration, why we measure in ppm instead of µmols, it would hopefully be interesting. :)

 

[Randy Holmes-Farley Verified Community Expert]

We should not use ppm since it is inherently flawed. Scientists use molar units.

It is straightforward, you just have to know how to do it.

mw nitrate (molecular weight) = 62 g/mole = 62 mg/mmol
mw phosphate = 95 g/mole = 95 mg/mmol

The short and rough estimate (which ignores the density of the seawater and equates ppm and mg/L) is to divide the weight based concentration (ppm) by the grams per mole.

1 ppm --> 1 mg/L

for nitrate:

1 ppm --> 1 mg/L / 62 mg/mmol = 0.016 mmole/L = 16 umole/L

 

[mcarroll]

Thanks!!! :)

molecular weight corresponds to atomic weight?

"Standard Atomic Weights:"

• Nitrogen – 14
• Phosphorus – 31
• Oxygen – 16

Nitrate = NO3 = (14 + (16 • 3)) = 62 mg/milli-mol
PO4 = (31 + (16 • 4)) = 95 mg/milli-mol

Got it so far, I think. :)

I tend to see nutrient nitrate concentration in the literature raised to 6.0 µmols/L fairly often.

To go backwards to ppm (for my test kits), I would go back to milli-mol, so:

6.0 µmols/L = 0.006 milli-mol/L​

And then convert to mg/L:

.006 milli-mol/L • 62 mg/milli-mol = .372 ppm​

Did I get that right?

 

[mcarroll]

6.0 µmol/L of PO4 would then be 0.57 ppm?

 

[Randy Holmes-Farley Verified Community Expert]

Molecular weight comes by adding up the atomic weights of the atoms in the molecule.

Yes, 6.0 µmol/L of PO4 ~ 0.57 ppm?

 

[mcarroll]

Thanks! This is going to be a huge help!! :)

 

[Randy Holmes-Farley Verified Community Expert]

You're welcome.

Happy Reefing. :)

 

[mcarroll]

We should not use ppm since it is inherently flawed. Scientists use molar units.

If I'm reading a modern scientific article about coral that uses mg/l or ppm rather than molar units, can I infer anything about the quality of the work, or in your estimation is that putting too much on it?

 

[Randy Holmes-Farley Verified Community Expert]

If I'm reading a modern scientific article about coral that uses mg/l or ppm rather than molar units, can I infer anything about the quality of the work, or in your estimation is that putting too much on it?

I'm not sure, but probably not. It might be more of an aquaculture "cultural thing".

 

[mcarroll]

Here's exactly how concentration of nitrogen is expessed in one article:
"above 5 μmol l−1"

Is that ≆ to "above 0.31 ppm" nitrate?

 

[Randy Holmes-Farley Verified Community Expert]

yes. :)

 

[mcarroll]

Sweet! :)

 

[mcarroll]

Oh...forgot my meta questions:

What exactly do the units mean as expressed?

I would write what I think they mean as: µmol/L

They use all lower case, no slash and what's the -1 for? It seems like I see almost all chemistry units expressed with a -1 at the end.

 

[nervousmonkey]

The -1 is used to designate that the unit with the -1 after it is the denominator. So 5 μmol l−1 is also equal to 5 μmol/l.

 

[Randy Holmes-Farley Verified Community Expert]

Yes, it means to the minus one power, or 1/unit. :)

L^(-1) = 1/L

 

[mcarroll]

Okay, it's time for my once-every-decade nitrate units conversion question!

Seems in fish literature there's a different standard for reporting nitrate than us and than the above examples which I think were in coral literatue.

For fish they seem to like mg/L of NO3-N.

If possible I'd like confirmation or correction on translating to ppm of NO3. I'm thinking it's a similar conversion as done earlier in the thread, but maybe not the same?

Goog say multiply mg/L NO3-N by 4.43 based on the atomic weight of the atoms.

So if I read that X fish is going to react badly to 250 mg/L NO3-N....is that the same as saying 1,108 ppm NO3?

I'm trying to read up on what levels of nitrate are actually verified as (acutely) harmful to fish but whenI do that conversion I'm getting these huge ppm NO3 numbers nowhere close to what anyone I've ever heard of getting in their tanks.....wondering if the numbers are correct of maybe the Goog is misleading me? :)

Thanks in advance....

 

[Dan_P]

Okay, it's time for my once-every-decade nitrate units conversion question!

Seems in fish literature there's a different standard for reporting nitrate than us and than the above examples which I think were in coral literatue.

For fish they seem to like mg/L of NO3-N.

If possible I'd like confirmation or correction on translating to ppm of NO3. I'm thinking it's a similar conversion as done earlier in the thread, but maybe not the same?

Goog say multiply mg/L NO3-N by 4.43 based on the atomic weight of the atoms.

So if I read that X fish is going to react badly to 250 mg/L NO3-N....is that the same as saying 1,108 ppm NO3?

I'm trying to read up on what levels of nitrate are actually verified as (acutely) harmful to fish but whenI do that conversion I'm getting these huge ppm NO3 numbers nowhere close to what anyone I've ever heard of getting in their tanks.....wondering if the numbers are correct of maybe the Goog is misleading me? :)

Thanks in advance....

NO3-N is nitrate nitrogen or the amount of nitrogen from a molecule of nitrate. Conversion is correct.

My impression is fish tolerate a boat load of nitrate.

 

[mcarroll]

NO3-N is nitrate nitrogen or the amount of nitrogen from a molecule of nitrate. Conversion is correct.

My impression is fish tolerate a boat load of nitrate.

Thank you!

Indeed on the boat load.

I'm learning, among other things, that public aquariums are dirty, nasty environments compared to our home aquariums. Yikes! (at least judging by NO3 levels)

In terms of acute toxicity, LC50 NO3 values for baby fish (including larvae, fry, fingerlings, juveniles) seem to range from astronomic to near-infinite....from a "low" of 800 ppm to as much as 22,000 ppm!! (some were seawater, some freshwater....doesn't seem to matter)

 

[Randy Holmes-Farley Verified Community Expert]

About 12 years ago, one of the Reerfcentral members who was a chemistry professor (he published the composition of NOPOX based on NMR in his lab) searched carefully on nitrate toxicity and the lowest marine LC50 he could find was 2200 ppm nitrate ion.

https://www.reefcentral.com/forums/showthread.php?t=2497914

 

[mcarroll]

About the same....

From: https://doi.org/10.1007/s11270-023-06260-5