Skimmers, Phosphate and Nitrate

[Heliman]

Recently I got an Ultral Low Phosphate Checker from Hanna...and I have had a play around with some parameters that for me have answered the question of "whether skimming removes Phosphates and Nitrates "

I have a certified check kit from Hanna to use with the ULR. This gave 1 ppb on my meter, the standard was 100 ppb plus or minus 5...so all was good.

I did 5 tests on my tank water and got (all in ppb) 8,8,11,8,9 of phosphorous
I took exactly 1 ml of my skimate and added this to the test vial and made it up to 10 ml with Ro/Di

I did 5 of these tests also and got 43,48,51,41,50 ppb of phosphorous

Extrapolating to the full 10 ml sample, the skimate corresponds to 387,432,459, 364, 450...ppb

The average of my tank tests was 8.8
The average of the skimate tests was 418

Corrected from ppb Phosphorous to ppm Phosphate (X 3.006 /1000) gives

Tank test 0.027 ppm
Skimate 1.28 ppm

A factor of 48 times as much PO4 in the skimate as in the DT

I think that answers the question for phosphates...now to try similar with Nitrates.

 

[gbru316]

I always thought skimming didn't directly remove no3 or po4, it removes the organics that break down to cause high no3 and po4.

 

[jerpa]

I always thought skimming didn't directly remove no3 or po4, it removes the organics that break down to cause high no3 and po4.

This is correct. It removes organics that would eventually break down and release phosphates. They still show up on the test because the organics still contain phosphates. It won't remove phosphates released into the water column from detritus that has already decayed.

 

[swcc]

Well the phosphate ends up there from organic removal, and also bacteria,algae, other microfauna, and phyto skimmed out.
Now this is the real key, to remove more po4 one should skim wet. By wet I mean with the foam produced in the top inch to inch and a half of the neck. One could skim very wet with the bubble column all the way up to the top, but, that is not completely necessary. Now, why is wet better?...the phosphate transporters I mentioned...they will die, live, or reproduce. if deposited in the neck, and they die, the non skimmable organics (such as PO4) can end up falling back into the water column. So, the best way for a skimmer to remove phosphate(and everything else it can) is to skim so most all skimmate ends up in the cup as opposed to crudding up the neck. If the water column is higher in the neck, less material is deposited and more is removed. Folks used to call wet skimming 'aggressive skimming'. Skimmate is not actually exported from the system till it ends up in the cup.

 

[acorral]

A good experiment would be dissolving some Phosphoric Acid (H3PO4) in RO/DI water and running a skimmer to test levels on the tank and skimmer cup.

My guess is skimmer won't remove a thing...

 

[Heliman]

A good experiment would be dissolving some Phosphoric Acid (H3PO4) in RO/DI water and running a skimmer to test levels on the tank and skimmer cup.

My guess is skimmer won't remove a thing...

Correct...the skimmer wont make bubbles in RO/DI......needs salt water for that....but the point is that it is likely the organic Phosphate that is going into the skimmer, the PO4 radical is bound to organic by-products within a hydrophillic molecule...hence it can be skimmed out. Unreacted PO4..existing as an ion is not likely to be removed by anything until it enters into an ionic or chemical combination with another chemical or organic substance.

Are you saying that Phosphates are NOT removed by skimming ??, the experimental (and published ) evidence suggests that it is. At what level it is removed from the water column is what interests me.

 

[steve9]

http://www.advancedaquarist.com/2010/2/aafeature

A well done study .......I know a big downdraft beckect
skimmer has always put a big dent in my po levels.

 

[acorral]

My point is much like SWCC said, phosphate is removed by skimming through organic removal.

The main purpose of lowering PO4 in the water column is with 2 objectives in mind:

-Starve nuisance algae
-Promote good calcification

Nuisance algae is fueled by mostly inorganic phosphate, also inorganic phosphate is the one that gets in the way of good calcification, so the real enemy is inorganic phosphate

That's why carbon dosing improves the removal of N and P (mostly N) from the water column because, by elimination of the carbon limiting factor, it promotes bacterial growth that binds inorganic N and P to organics that are later removed by skimming in the form of organics.

Would be interesting to do the same test but also using organic carbon dosing and see how those numbers are affected

 

[mattyp54]

That Hannah checker is a little different look up on YouTube how to use them there are a few little tricks the directions don't tell you

 

[keithhays]

It sounds like there are two different conversations or at least there should be two conversations. The protein skimmer can remove sources of bound phosphate (prior to breaking down) after that breakdown something like GFO will be needed to remove the no longer bound phosphate. Since it is unlikely that all bound phosphate sources will be caught prior to break down, both items are needed.

 

[mattyp54]

That's how my tank is I need to have both a high quality skimmer and run the high capacity gfo from brs to get the tank right