Aragonite Sand And Phosphate Adsorption

[Randy Holmes-Farley Verified Community Expert]

I’m not sure I see a reason to slow up, it’s just that there is more to be bound for each 0.1 ppm drop as you get lower and lower.

 

[Dan_P]

Sorry to revive an old thread but didnt want to strt a new one.

I am trying to understand this whole thing. I am currently dosing LC and my tank will not go below .4-.5 ppm po4. Is the correct understand that it seems thats a significant breakpoint?

The PO4 adsorption is fairly straightforward. More PO4 will bind to aragonite as the concentration increases, though it is not quite linear.

Desorbing PO4 from aragonite does not quite follow the adsorption curve in reverse but there is no discontinuity like a breakpoint.

If PO4 reduction seems to have stalled, it is not because of the adsorbed PO4 being dumped at an increased rate at this concentration. Assuming no errors in measurements or LC additions, we would have to think more along the line that PO4 production has recently increased for some random reason which consumes the LC. Or how about testing error? Do you know if lanthanum phosphate particles cause the phosphate tests to read high? This might turn out to be one of those forehead slapping incidents.

 

[ReefHunter006]

The PO4 adsorption is fairly straightforward. More PO4 will bind to aragonite as the concentration increases, though it is not quite linear.

Desorbing PO4 from aragonite does not quite follow the adsorption curve in reverse but there is no discontinuity like a breakpoint.

If PO4 reduction seems to have stalled, it is not because of the adsorbed PO4 being dumped at an increased rate at this concentration. Assuming no errors in measurements or LC additions, we would have to think more along the line that PO4 production has recently increased for some random reason which consumes the LC. Or how about testing error? Do you know if lanthanum phosphate particles cause the phosphate tests to read high? This might turn out to be one of those forehead slapping incidents.

Doesnt that imply you could overdose LC if the test is wrong. Do you suggest running the tests differenly?

 

[Randy Holmes-Farley Verified Community Expert]

Doesnt that imply you could overdose LC if the test is wrong. Do you suggest running the tests differenly?

Not sure how people are deciding on a lanthanum dose, but the binding to aragonite makes one need a lot more to get a particular drop than a mole equivalent concentration suggests.

 

[ReefHunter006]

Not sure how people are deciding on a lanthanum dose, but the binding to aragonite makes one need a lot more to get a particular drop than a mole equivalent concentration suggests.

Thats understandable, I took his comment to imply that if the test kit registers the Lanthanum Phosphate then someone could potentially dose lanthanum even though all phosphate is bound and unusable causing potential issues.

Which made me wonder if there is a proper way to dose to avoid that issue.

 

[Dan_P]

Doesnt that imply you could overdose LC if the test is wrong. Do you suggest running the tests differenly?

One safeguard against particulate contamination (which is what I had in mind) is to pass test samples through a syringe filter, 0.45 or 0.22 micron. If this makes no difference, then we need a new hypothesis.

 

[ReefHunter006]

One safeguard against particulate contamination (which is what I had in mind) is to pass test samples through a syringe filter, 0.45 or 0.22 micron. If this makes no difference, then we need a new hypothesis.

Are lan. phos. particles bigger than inorganic phos or any other bound up phos?

 

[Dan_P]

Are lan. phos. particles bigger than inorganic phos or any other bound up phos?

I don’t know, but they must be big enough to be captured by filter socks, so, I guess that’s comparable to say calcium phosphate particles.

 

[areefer01]

One safeguard against particulate contamination (which is what I had in mind) is to pass test samples through a syringe filter, 0.45 or 0.22 micron. If this makes no difference, then we need a new hypothesis.

That is an interesting thought. I can say that when I am using a hammer to lower phosphates, LC, it drops quickly then will rebound the next day between .07 and .10 ppm. I will let it go a couple of days then knock it down again. I do not believe the precipitate (if that is what the cloudy bit left behind) affects the test results or I would expect a different pattern.

Unfortunately my testing is automated so I can't do the filter test but I am intrigued. I have had a needs cleaning message before and that is cleared by running some bleach through the system. That is typically seen when nitrates are trending higher. I'll have to check the data the next time it happens.

Edit: I left off that my rocks, or substrate, or both have phosphate bound/stored which is why I see the immediate rebound. I saw the same pattern when using GFO. I prefer LC because it is more cost effective with my levels and less work to use.

 

[Randy Holmes-Farley Verified Community Expert]

Thats understandable, I took his comment to imply that if the test kit registers the Lanthanum Phosphate then someone could potentially dose lanthanum even though all phosphate is bound and unusable causing potential issues.

Which made me wonder if there is a proper way to dose to avoid that issue.

I expect the solids settle out in most tanks, but allowing a sample to settle before testing might avoid detecting solids.

 

[Randy Holmes-Farley Verified Community Expert]

Are lan. phos. particles bigger than inorganic phos or any other bound up phos?

I’m certain there is a wide range of sizes.