Dehydrating to concentrate water samples

[Heathcliff37]

Is it possible to dehydrate water samples to concentrate certain ions such as nitrate or phosphate to allow more precise low range measurements, similar to how dilutions are possible when concentrations are too high to measure?

I understand certain parameters, such as calcium and magnesium, would start to precipitate, but wouldn’t phosphate and nitrogenous compounds stay relatively unreacted?

If so, what would be the most efficient way to do this? Boiling? Leaving outside in the sun? A food dehydrator?

Thank you.

 

[blaxsun]

Get a Hanna ultra low range checker.

 

[Reefinmike]

Short answer- No, it won’t work. If you want better precision, accuracy and resolution you should develop consistent testing procedures and buy good tests. I own a few of the best regarded hanna checkers… they’re ok for colorblind people but otherwise far from “good”. If you have decent eyes, the red sea pro no3/po4 test is incredible at ultra low levels. With some familiarity, it’s easy to “split the difference” for colors in between.

regarding testing procedure-

-Do dropper bottle reagents sometime have a half drop because of a bubble for the first drop? Or is every drop compromised because of a lingering bubble on the tip? drip the first drop on a square of toilet paper or dab the tip with a q-tip before dripping in your vial. Keeping all dropper bottles stored upright will resolve most issues.
-use a magnetic stirrer and a timer
-level off scoops of powder reagent
-double testing volume and reagents for higher resolution using color indicated endpoint titrations. Don’t use this technique on color gradient dependent tests.
-clean everything immediately and very well. Ca, mg and K kits often leave a precipitate that needs scrubbed or acid washed. Phosphate/orous tests often stain the vial green/blue without regular scrubbing. Rinse everything in rodi(including syringe tips, syringes, caps, stir bars) and let dry away from potential contamination.


I spent a couple years experimenting with different kits. Most important to least, I analyzed them by:
1-Precision(test to test repeatability)
2-Cause and effect reactivity( testing a sample 3x in a row, adding x.xx ppm of a carefully weighed dry chem and testing again 3x. Does the test accurately show the amount I dosed?)
3-Ease of use(“work” time/test, tesious nature, and ease of cleanup)
4-Accuracy(how close it is to the actual number)
5-Cost

There’s no mystery behind reef chemistry. i’ve decided these will be my “forever kits”. Even made a little tray to hold everything and limit box fumbling. In the right order, I can test, record and cleanup- Specific gravity, calcium, alkalinity, magnesium, potassium, nitrate and phosphate in 25 minutes.



-Sg- Tropic marin hydrometer is leagues better than any other device.

-Ca, alk, Mg, K- salifert. Simple, cheap, reliable and accurate

-NO3/PO4- red sea pro “algae control kit” is extremely accurate and precise. Really shines at ultra low levels < 4.0/0.16ppm

pH- apex probe. Please don’t waste any money or time on drop style(hanna included) pH test kits. They’re terribly inaccurate

 

[Randy Holmes-Farley Verified Community Expert]

Is it possible to dehydrate water samples to concentrate certain ions such as nitrate or phosphate to allow more precise low range measurements, similar to how dilutions are possible when concentrations are too high to measure?

I understand certain parameters, such as calcium and magnesium, would start to precipitate, but wouldn’t phosphate and nitrogenous compounds stay relatively unreacted?

If so, what would be the most efficient way to do this? Boiling? Leaving outside in the sun? A food dehydrator?

Thank you.

No, this is not a good plan for phosphate because however you do it may end up precipitating calcium carbonate, and that will take out phosphate with it.

You may be able to do it for nitrate, but if you need to do it, nitrate is probably too low already.

 

[Randy Holmes-Farley Verified Community Expert]

-Sg- Tropic marin hydrometer is leagues better than any other device.

You mean better than any other cheap hobby device?

It's certainly not better than a high end conductivity meter. The practical salinity scale is based on conductivity and not specific gravity for a reason: better precision and accuracy than hydrometers, refractometers, or other methods used.

 

[Heathcliff37]

No, this is not a good plan for phosphate because however you do it may end up precipitating calcium carbonate, and that will take out phosphate with it.

You may be able to do it for nitrate, but if you need to do it, nitrate is probably too low already.

Does the precipitation of calcium carbonate take out a significant amount of phosphate?

I know absorption onto aragonite is pH dependent, so what if we just added some acid, like HCl, to lower absorption? That would also prevent calcium phosphate from precipitating. Could that reduce the phosphate “taken out” to be roughly within a 0.04ppm margin of error which is standard for Hanna and most tests?

Regarding nitrate, I’m confused. Don’t you recommend keeping it below 0.2 ppm (http://www.reefkeeping.com/issues/2004-05/rhf/index.htm), while most nitrate tests have an accuracy rating greater than that? For example, the Hanna Nitrate Low Range Checker has an accuracy rating of 0.25 ppm, so using it without concentrating the sample, we could never know if we are below the recommendation of 0.2 ppm

 

[Heathcliff37]

Short answer- No, it won’t work. If you want better precision, accuracy and resolution you should develop consistent testing procedures and buy good tests. I own a few of the best regarded hanna checkers… they’re ok for colorblind people but otherwise far from “good”. If you have decent eyes, the red sea pro no3/po4 test is incredible at ultra low levels. With some familiarity, it’s easy to “split the difference” for colors in between.

regarding testing procedure-

-Do dropper bottle reagents sometime have a half drop because of a bubble for the first drop? Or is every drop compromised because of a lingering bubble on the tip? drip the first drop on a square of toilet paper or dab the tip with a q-tip before dripping in your vial. Keeping all dropper bottles stored upright will resolve most issues.
-use a magnetic stirrer and a timer
-level off scoops of powder reagent
-double testing volume and reagents for higher resolution using color indicated endpoint titrations. Don’t use this technique on color gradient dependent tests.
-clean everything immediately and very well. Ca, mg and K kits often leave a precipitate that needs scrubbed or acid washed. Phosphate/orous tests often stain the vial green/blue without regular scrubbing. Rinse everything in rodi(including syringe tips, syringes, caps, stir bars) and let dry away from potential contamination.


I spent a couple years experimenting with different kits. Most important to least, I analyzed them by:
1-Precision(test to test repeatability)
2-Cause and effect reactivity( testing a sample 3x in a row, adding x.xx ppm of a carefully weighed dry chem and testing again 3x. Does the test accurately show the amount I dosed?)
3-Ease of use(“work” time/test, tesious nature, and ease of cleanup)
4-Accuracy(how close it is to the actual number)
5-Cost

There’s no mystery behind reef chemistry. i’ve decided these will be my “forever kits”. Even made a little tray to hold everything and limit box fumbling. In the right order, I can test, record and cleanup- Specific gravity, calcium, alkalinity, magnesium, potassium, nitrate and phosphate in 25 minutes.



-Sg- Tropic marin hydrometer is leagues better than any other device.

-Ca, alk, Mg, K- salifert. Simple, cheap, reliable and accurate

-NO3/PO4- red sea pro “algae control kit” is extremely accurate and precise. Really shines at ultra low levels < 4.0/0.16ppm

pH- apex probe. Please don’t waste any money or time on drop style(hanna included) pH test kits. They’re terribly inaccurate

Thank you for the recommendations! I too am very careful with my testing procedures.

 

[Heathcliff37]

Get a Hanna ultra low range checker.

It's so expensive!

 

[Randy Holmes-Farley Verified Community Expert]

Does the precipitation of calcium carbonate take out a significant amount of phosphate?

I know absorption onto aragonite is pH dependent, so what if we just added some acid, like HCl, to lower absorption? That would also prevent calcium phosphate from precipitating. Could that reduce the phosphate “taken out” to be roughly within a 0.04ppm margin of error which is standard for Hanna and most tests?

Regarding nitrate, I’m confused. Don’t you recommend keeping it below 0.2 ppm (http://www.reefkeeping.com/issues/2004-05/rhf/index.htm), while most nitrate tests have an accuracy rating greater than that? For example, the Hanna Nitrate Low Range Checker has an accuracy rating of 0.25 ppm, so using it without concentrating the sample, we could never know if we are below the recommendation of 0.2 ppm

Yes, or I would not have mentioned it.

Calcium carbonate takes out a lot of phosphate if there's a significant amount in the water.

The article above is older (2004) and stems from when we were more trying to mimic the ocean. Tanks do better at 2-10 ppm nitrate, and that's what I've been recommending for a number of years.

 

[Reefinmike]

You mean better than any other cheap hobby device?

It's certainly not better than a high end conductivity meter. The practical salinity scale is based on conductivity and not specific gravity for a reason: better precision and accuracy than hydrometers, refractometers, or other methods used.

You are absolutely correct as always! I recall you explaining to me the difference between methods, why conductivity is the standard in the scientific field. You also corrected me on why you can’t get an accurate reading by measuring a liter of saltwater, boil off all the water and weigh the remaining salt. Some elements are volatile and boil off!

but yeah, I “feel” the big hydrometer is the best hobby level measurement.

 

[Heathcliff37]

Yes, or I would not have mentioned it.

Calcium carbonate takes out a lot of phosphate if there's a significant amount in the water.

The article above is older (2004) and stems from when we were more trying to mimic the ocean. Tanks do better at 2-10 ppm nitrate, and that's what I've been recommending for a number of years.

Interesting. Do you have an updated post about your recommended parameters? What do you recommend for phosphate?

 

[Randy Holmes-Farley Verified Community Expert]

Interesting. Do you have an updated post about your recommended parameters? What do you recommend for phosphate?

Most things have not changed since this article came out,

Optimal Parameters for a Coral Reef Aquarium: By Randy Holmes-Farley

[note: edited on 5/29/2022 to update the nitrate and phosphate sections with higher recommended levels.] One of the main roles of an aquarist with a coral reef aquarium is to ensure that the conditions are right for their tank inhabitants. There are many different attributes of the aquarium...

www.reef2reef.com

but I presently recommend 2-10 ppm nitrate (unless you are dosing ammonia or amino acids) and 0.02 to 0.1 ppm phosphate.

One of the reasons to not recommend the lower levels is increased prevalence of dinos and the risk factor from low nutrients.

 

[Dan_P]

Does the precipitation of calcium carbonate take out a significant amount of phosphate?

I know absorption onto aragonite is pH dependent, so what if we just added some acid, like HCl, to lower absorption? That would also prevent calcium phosphate from precipitating. Could that reduce the phosphate “taken out” to be roughly within a 0.04ppm margin of error which is standard for Hanna and most tests?

Regarding nitrate, I’m confused. Don’t you recommend keeping it below 0.2 ppm (http://www.reefkeeping.com/issues/2004-05/rhf/index.htm), while most nitrate tests have an accuracy rating greater than that? For example, the Hanna Nitrate Low Range Checker has an accuracy rating of 0.25 ppm, so using it without concentrating the sample, we could never know if we are below the recommendation of 0.2 ppm

Interesting conversation. I tried this years ago with nitrate. Here are some additional thoughts.

If you have time on your hands go ahead and try your idea. Blowing air over a water sample will concentrate it. This is the time consuming part of the idea and it might be a deal breaker if you are impatient.

PO4

In addition to what Randy said, the salinity reaches a point where lots of salts come out of solution. If you go to dryness and then add enough RO/DI for a test, everything will not go back into solution. Then there is the problem that the phosphate test might have been developed for a certain salinity, alkalinity and silicate content, which is all higher for the concentrated sample. The other potential problem is that other concentrated ions might now be at concentrations that interfere with the test. This is so messy to figure out whether it would work, I would just go ahead and run the experiment.

NO3

The nitrate test is sensitive to salinity. The test gives higher readings when the salinity is decreased. This is not an automatic kill of your idea, it means at a minimum, the test will likely give a low reading. Again, just do the experiment or you will be wondering about it your whole life

There are a couple things to increase sensitivity, but they are not free.

Increasing the path length of light that passes through the sample.

For Hanna PO4, I don’t think this will work because the limit of detection for this chemistry might not be low enough. I haven’t tried this (@taricha) but I think the color possibly disappears before 0 ppm. In the case of the nitrate test, increasing the path might allow you to detect lower concentrations.

Increase the amount of zinc in the nitrate test.

The nitrate sensitivity in our test kits is likely limited by the amount of zinc supplied in the reagent. Increasing the amount should squeeze out a bit more sensitivity. I haven’t done this but I am encouraged that it will work based on the Hanna low range test. It has a large amount if zinc dust.
Pyrotechnic grade zinc dust is cheap.

 

[taricha]

NO3

The nitrate test is sensitive to salinity. The test gives higher readings when the salinity is decreased. This is not an automatic kill of your idea, it means at a minimum, the test will likely give a low reading. Again, just do the experiment or you will be wondering about it your whole life

There are a couple things to increase sensitivity, but they are not free.

Increasing the path length of light that passes through the sample.

For Hanna PO4, I don’t think this will work because the limit of detection for this chemistry might not be low enough. I haven’t tried this (@taricha) but I think the color possibly disappears before 0 ppm. In the case of the nitrate test, increasing the path might allow you to detect lower concentrations.

one encouraging thing on the NO3, hanna LR NO3 has a precipitation/filtration step, reagent A is high pH and precipitates a lot of stuff out of solution anyway, runs the zinc step in the sample with this precipitate and then filters it all out. So it's quite possible this test would be able to withstand increasing the concentration by evaporation since it removes the precipitable material anyway.

hanna PO4, there is absorbance formed by the test at levels below where your eye can detect it as blue and below where your checker can quantify it. So longer path length could help. Also - the absorbance is actually better at longer wavelength, like 600nm+.

 

[Heathcliff37]

one encouraging thing on the NO3, hanna LR NO3 has a precipitation/filtration step, reagent A is high pH and precipitates a lot of stuff out of solution anyway, runs the zinc step in the sample with this precipitate and then filters it all out. So it's quite possible this test would be able to withstand increasing the concentration by evaporation since it removes the precipitable material anyway.

hanna PO4, there is absorbance formed by the test at levels below where your eye can detect it as blue and below where your checker can quantify it. So longer path length could help. Also - the absorbance is actually better at longer wavelength, like 600nm+.

I think the precipitates formed after the addition of a high pH reagant are different than those formed by simple evaporation. It’s then a matter of whether or not any of these precipitants affect nitrate.

I’m not exactly sure what you mean regarding the Hanna checker, but it sounds like a research grade laboratory photometer would solve the issue. With any small relatively cheap hobbiest device there are going to be drawbacks.

 

[Heathcliff37]

Most things have not changed since this article came out,

Optimal Parameters for a Coral Reef Aquarium: By Randy Holmes-Farley

[note: edited on 5/29/2022 to update the nitrate and phosphate sections with higher recommended levels.] One of the main roles of an aquarist with a coral reef aquarium is to ensure that the conditions are right for their tank inhabitants. There are many different attributes of the aquarium...

www.reef2reef.com

but I presently recommend 2-10 ppm nitrate (unless you are dosing ammonia or amino acids) and 0.02 to 0.1 ppm phosphate.

One of the reasons to not recommend the lower levels is increased prevalence of dinos and the risk factor from low nutrients.

Thank you!