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View Full Version : does heavy skimming remove PO4 and/or NO3?


mathman7728
11/09/2017, 11:29 AM
as the title says, will skimming cause a drop in P04 and/or NO3. for example, i have high NO3 but .04-.06 PO4 (which is think is a good level for mixed reef) and wondered if skimming more reduce NO but no PO?

thank you!

Optionman
11/09/2017, 11:50 AM
i think the answer is no but i'll wait and see what others say

hkgar
11/09/2017, 11:59 AM
The short answer is no.

The long answer is noooooo.

They remove dissolved organics, like fish poop.

http://reefkeeping.com/issues/2002-06/fm/feature/index.htm

tmz
11/09/2017, 12:11 PM
Skimming does not remove PO4 or NO3 directly; but, does remove organics which might otherwise decay in the tank adding inorganic N and P as a result.

mcgyvr
11/09/2017, 01:59 PM
Skimming does not remove PO4 or NO3 directly; but, does remove organics which might otherwise decay in the tank adding inorganic N and P as a result.

^^That..
Skimming will never reduce your current nitrate or phosphate levels.. But it can keep them from going higher...

bertoni
11/09/2017, 03:08 PM
Dissolved nutrients generally can't be removed by skimming. Phosphate can be removed only at an interesting rate if it's still attached to an organic. :) Of course, any skimmer will remove a bit of the water column, which amounts to an incredibly tiny water change.

lilphil26
11/09/2017, 07:54 PM
I do believe the skimmer will remove phosphate and nitrate but not directly. People that carbon dose do indeed see increased skimmate production and it's thought that the bacteria which are feeding off the phosphate and nitrate are a part of the skimmate that you collect.

tmz
11/09/2017, 08:58 PM
The bacteria are organic and consume dissolved Nand P and do seem to be caught in the air/water space between the skimmer bubbles and most amphipathic organics are.

Dan_P
11/10/2017, 03:01 AM
I can detect phosphate, ammonia and nitrate in the skimmate. The nitrate level in the skimmate seems to be correlated to the amount in the aquarium water. I assume this means it is not concentrated but carried over. Recently, I measured ammonia between 0.5-8 ppm in foamate. Concentrating ammonia might happen through the skimming of a large organic acid salt of ammonia, though I have not investigated why an ammonium salt would exist in a sea of sodium ions. Another explanation is that the salicylate test is detecting an organic amine. Skimming also captures microalgae (skimmate fluoresces under long wavelngth UV) and bacteria. Maybe test conditions break open the cells, releasing ammonia. Since fresh skimmate also shows ammonia, it is probably not due to bacteria metabolism after the skimmate is collected though I am still not a 100% convinced. Phosphate is detected in the 0.2-2 ppm range and might be concentrated with a large basic organic molecule or comes over in the shells of phytoplankton. Support for the latter notion is that acidifying the solid in the skimmate with dilute HCl for five minutes generated twice the amount of dissolved phosphate than in the liquid. Also, the phosphate test conditions might be acidic enough to dissolve some of this solid, giving the illusion of dissolved phosphate. Overall, a skimmer removes nitrogen and phosphorous in amounts that are useful but not substantial. Given the volume of skimmate my skimmer collects per day, phosphate is reduced in the aquarium by 0.001 ppm per day.

tmz
11/10/2017, 09:36 AM
The water a protein skimmer pushes to the cup will pass along some small amounts of dissolved nutrients like a very small water change will as Jon noted.

The rising flow action in the skimmer will also push along bits of this and that algae detritus bacteria etc.

However, the foam fractionation function( the actual "skimming") relies on the attraction of organic molecules to water and their repulsion from it. Amphipathic molecules like proteins and others with bi-polarity are pulled toward the water on one side and repelled by it on the other. These ampipathic molecules are most susceptible to removal via skimming as they get cling to the air and water surface there at the same time and get trapped between the bubbles.

Leopardshark
11/10/2017, 02:29 PM
The short answer is no.

The long answer is noooooo.



:thumbsup:

bertoni
11/10/2017, 03:37 PM
Oops, I should have posted this article:

http://reefkeeping.com/issues/2006-08/rhf/index.php

Dan_P
11/10/2017, 04:05 PM
The water a protein skimmer pushes to the cup will pass along some small amounts of dissolved nutrients like a very small water change will as Jon noted.

The rising flow action in the skimmer will also push along bits of this and that algae detritus bacteria etc.


Very small particles like bacteria and phytoplankton are not pushed along but rather experience similar forces as molecules that adhere to the water air interface. Shine a black light on skimmate and you are likely to see it fluoresce due to all the phytoplankton chlorophyll. This amount of phytoplankton would not accumulate by entrainment of debris in the aquarium water. In addition, some of the solids or slime seen in the skimmate are likely material that has agglomerated or precipitated as a result being concentrated in the foam.

Subsea
11/10/2017, 06:41 PM
Skimming does not remove PO4 or NO3 directly; but, does remove organics which might otherwise decay in the tank adding inorganic N and P as a result.

By organics, would that include free swimming bacteria?

PS. I jumped in to soon as I see that the answer for bacteria was already covered.

Subsea
11/10/2017, 06:52 PM
as the title says, will skimming cause a drop in P04 and/or NO3. for example, i have high NO3 but .04-.06 PO4 (which is think is a good level for mixed reef) and wondered if skimming more reduce NO but no PO?

thank you!

Of course skimming reduces both nitrate and phosphate. While difficult to analyze it is mostly composed of bacteria which should line up with the Redfield Ratio.

Why do you ask about the ratio of nitrate to phosphate?

What do you call high nitrate?

tmz
11/11/2017, 08:39 AM
Very small particles like bacteria and phytoplankton are not pushed along but rather experience similar forces as molecules that adhere to the water air interface.


Why do you exclude upward flow as a force moving organics and small particulate matter upward. Upwelling is a part of how reefs work. Amphipathic and hydrophobic planktonic microrganisms and particulate matter are attracted to the air water interfaces but that does not exclude the effect of upward flow on them.

Dan_P
11/11/2017, 05:47 PM
Very small particles like bacteria and phytoplankton are not pushed along but rather experience similar forces as molecules that adhere to the water air interface.


Why do you exclude upward flow as a force moving organics and small particulate matter upward. Upwelling is a part of how reefs work. Amphipathic and hydrophobic planktonic microrganisms and particulate matter are attracted to the air water interfaces but that does not exclude the effect of upward flow on them.

The upwelling of water in the ocean moves bulk water and it's contents to other regions. If the other region is lower in organic content, the concentration increases when the richer water is mixed in. It does not act at the molecular level to preferentially "move" molecules or at the micron level to move sub micron particles.

In the case of a skimmer, the upwelling is not water but air in the form of tiny bubbles. Aquarium water mixes with the bubbles and rises with the air into the skimmer throat. It is still just aquarium water mixed with air. Nothing additional has been swept along because there is nothing additional brought along but the material in the aquarium water. So very wet skimming is barely different from a water water change. The upward movement of water in the skimmer, the water entrained in the foam, is doing nothing to change the material concentration as it moves higher up in the skimmer column or skimmer thoat. The concentration of material we observe in skimmate is a result of the bubble breakage and the concentrated material reentering the water in the foam and re-attaching to bubbles, strengthening them which results in them lasting longer and eventually leaving the skimmer throat top. In addition, the water entrained in the foam drains away in the skimmer throat, also giving a dryer, more concentrated foam. Upward flow by itself is not part of the foam fractionation mechanism of concentration of molecules and particulates.

tmz
11/13/2017, 12:43 PM
The upwelling is water moving with the bubbles . Most skimmers create a significant upward flow . Reef's move water upward via advective flow.
The differentiation between upward flow and foam fractionation was clear in my earlier post. Nonetheless ,a"bit" of unbound material will move in an upward flow and some of that ,probably a small amount will settle in the skimmate, in my view.


This from Randy's article previously cited explains it better:




[B]"...The froth of bubbles begins to drain under gravity, removing much of the water between the bubbles. Some of the bubbles merge into larger bubbles. As long as the bubbles do not pop before significant draining occurs, then the organics will be left behind in the foam, along with some residual water. Eventually, the concentration of organics on the top of the foam becomes great enough that they exceed the solubility limit, and small particulates of organics form. These particulates are generally what a skimmer collects, along with some water and organics that remain present in solution or at the air/water interface...."[B]

So, I don't think all of the material in the skimmate results from molecular attachment at the air water interface ; some albiet arguably a very small amount can be pushed along with the water .

orcafood
11/13/2017, 11:51 PM
After adding nori or ground shellfish to my tank, I definitely see it start to rise out of the collection cup on my recirc skimmer. I’d argue that the upflow of bubbles as well as solubilty characteristics of the bubble interface both aid in this effect. Watching the top of the skimmer bubbles closely, in certain cases I have seen the organics dancing across the bubble surface and precipitate! Surely a better name for protein skimmers would be surfactant skimmer :)

Carbon dosing definetly sequesters no3 and po4 into skimmable microorganisms. Skimming cannot remove appreciable amounts of inorganic nutrients like no3 or po4, but is excellent at removing organic nutrients as they contain surfactant like qualities. Microorganisms are covered in negative surfactants. If the quantity of surfactants drops below a critical concentration, the foam level falls.

Measuring nitrate or phosphate in skimmate is likely useless. Microorganisms are both growing and dying/lysing in the skimmate shuffling nutrients between organic and inorganic states.

tmz
11/14/2017, 09:59 AM
That's how I view it : nicely stated. I've also seen "bits of this and that " in skimmate cup and the skimmer water column.

Decaying organics there will release nutrients and other elements; some consumption might also occur;measurements likely chart a false trail

Dan_P
11/14/2017, 04:08 PM
After adding nori or ground shellfish to my tank, I definitely see it start to rise out of the collection cup on my recirc skimmer. I’d argue that the upflow of bubbles as well as solubilty characteristics of the bubble interface both aid in this effect.

You could argue that the upflow of bubbles was a contributing factor but you will find no scientific research to back up your arguement. The operation of foam fractionation and froth flotation are understood and “up flow” per se has nothing to do with the mechanism by which these devices separate hydrophobic material from water. If you ran a foam fractionator in outer space, i.e., zero G, where there is no up flow, it would work just as well, though I doubt anyone has.

tmz
11/15/2017, 09:11 AM
Ehtereal agumments and black holes aside, simply stated flowing water moves material on earth;skimmer's create significant upward flow; whether or not the movement of a particular particle is aided by foam fractionation depends on the amphipathic qaulity of the particle.

Dan_P
11/15/2017, 03:50 PM
Ehtereal agumments and black holes aside, simply stated flowing water moves material on earth;skimmer's create significant upward flow; whether or not the movement of a particular particle is aided by foam fractionation depends on the amphipathic qaulity of the particle.

Sure, what you state is true, flowing water moves things, and skimmer flow moves upwards, but all this is not really relevant in discussing how skimmers operate, that is, how they concentrate material and how things end up in the collection cup. If by chance a particle is caught in the flow, it could end up in the collection cup. And if this chance occurrence is what you are talking about, then OK!

orcafood
11/15/2017, 10:44 PM
If there is no gravity, bubbles would not rise. I would guess a skimmer in outer space would not work. Heck holding water in a cup in outer space wouldn't work.

On a scientific note, if I put my face above my skimmer collection cup, I can feel air flowing out at a very appreciable rate.

You could argue that the upflow of bubbles was a contributing factor but you will find no scientific research to back up your arguement. The operation of foam fractionation and froth flotation are understood and “up flow” per se has nothing to do with the mechanism by which these devices separate hydrophobic material from water. If you ran a foam fractionator in outer space, i.e., zero G, where there is no up flow, it would work just as well, though I doubt anyone has.

tmz
11/16/2017, 09:30 AM
Sure, what you state is true, flowing water moves things, and skimmer flow moves upwards, but all this is not really relevant in discussing how skimmers operate, that is, how they concentrate material and how things end up in the collection cup. If by chance a particle is caught in the flow, it could end up in the collection cup. And if this chance occurrence is what you are talking about, then OK!

That's what I said in post #10. Upward flow is part of what skimmers do;so is aeration btw:


The water a protein skimmer pushes to the cup will pass along some small amounts of dissolved nutrients like a very small water change will as Jon noted.

The rising flow action in the skimmer will also push along bits of this and that algae detritus bacteria etc.

However, the foam fractionation function( the actual "skimming") relies on the attraction of organic molecules to water and their repulsion from it. Amphipathic molecules like proteins and others with bi-polarity are pulled toward the water on one side and repelled by it on the other. These ampipathic molecules are most susceptible to removal via skimming as they get cling to the air and water surface there at the same time and get trapped between the bubbles.


I have no idea why you chose to contradict it in absolute terms.



The movement of particulate matter via flow is relevant to the OPs question about nutrient removal and a part ,albeit perhaps a small one, of the way skimmers operate. Some of the bits of material moved along by the flow to the cup would otherwise decay or dissolve in the tank and do also account for some of the content of the skimmate.

Dan_P
11/16/2017, 01:24 PM
That's what I said in post #10. Upward flow is part of what skimmers do;so is aeration btw:


The water a protein skimmer pushes to the cup will pass along some small amounts of dissolved nutrients like a very small water change will as Jon noted.

The rising flow action in the skimmer will also push along bits of this and that algae detritus bacteria etc.

However, the foam fractionation function( the actual "skimming") relies on the attraction of organic molecules to water and their repulsion from it. Amphipathic molecules like proteins and others with bi-polarity are pulled toward the water on one side and repelled by it on the other. These ampipathic molecules are most susceptible to removal via skimming as they get cling to the air and water surface there at the same time and get trapped between the bubbles.


I have no idea why you chose to contradict it in absolute terms.



The movement of particulate matter via flow is relevant to the OPs question about nutrient removal and a part ,albeit perhaps a small one, of the way skimmers operate. Some of the bits of material moved along by the flow to the cup would otherwise decay or dissolve in the tank and do also account for some of the content of the skimmate.

I see your point and I agree with Jon. I appreciate your added clarification of “albeit perhaps a small one”. In skimmer mechanism terms, the upper limit of removal of bacteria, detritus, etc by the entrained water is equivalent to that of a water change of the same volume, no more. My point, water flow simply cannot concentrate material like a broom might sweep up dirt from all over to one spot on the floor. Yeah, so no arguement I guess.

orcafood
11/17/2017, 12:35 AM
I see your point and I agree with Jon. I appreciate your added clarification of “albeit perhaps a small one”. In skimmer mechanism terms, the upper limit of removal of bacteria, detritus, etc by the entrained water is equivalent to that of a water change of the same volume, no more. My point, water flow simply cannot concentrate material like a broom might sweep up dirt from all over to one spot on the floor. Yeah, so no arguement I guess.

I feel it is hard to compare a water change with wet skimming. Water changing takes out clear water whereas when I wet skim and replace the water with clean salt water I replace tea colored skim with clear saltwater. Though the bubble interface itself may not hold much inorganic nutrients, I bet that the hydration shell around the bubble interface would hold larger amounts of inorganic nutrients. Like dissolves like :) In the past I have performed minute water changes with heavy wet skimming to great effect.

I also don't agree with the upwards air flow in a skimmer being a small effect, though I do have a beast of a skimmer, akin to a SRO-5000. Maybe with recirculating skimmers the effect is more pronounced, especially when fed directly from the tank overflow? I feed the output of my skimmer directly into a 20 gallon settling tank and have yet to find small bits of food or ground shellfish in the settling tank. I do find it in my skimmer collection cup though, and can watch it be removed after feeding in real time. This leads me to believe that the skimmer does a great job of removing macro-particles of ground seafood and nori. I doubt the electronic/polarity effects are outweighing the macro-forces in this circumstance, and I feed quite a bit.

Back to the original question: with proper carbon dosing, a skimmer can remove nitrate and phosphate. But it is possible that they may not be removed in the proper ratio. This can be solved with water changes. I always liked wet-skimming, then adding salt to the replacement water, almost like a mini water change every day to bring the nutrients back into sync. This question is a bit loaded, as I feel smaller skimmers are less likely to pull out larger particulate, especially if they are not fed directly by the tank drain.

tmz
11/17/2017, 09:24 AM
I think whether the effect of upward flow is perhaps small or larger depends on the flow rate of the skimmer ,the type of the skimmer whether it's running dry or wet and where it is located in terms of proximate detritus and other particulate matter.
Anecdotally,
I run two large skimmers( ASM 4xx) , each with a sedra 1500pump,each in sump with semi full cup water changes 2x per week or so There is almost no buildup of detritus and other matter in these sumps while there is quite a bit in other low lying reservoirs in the system .
My integrated system includes 7 tanks and 5 reservoirs (3 for cryptic refugia two for sumps);3 display tanks are on the first floor of my home; the sumps,refugia are on the basement floor; the other four tanks are on 3 foot high stands in the basement.

I also notice buildups around powerhead inlets and on the bottom of tanks under powerheads as the draw from the powerheads moves it there ;seems like the water intake on the skimmer would have the same effect.

tmz
11/17/2017, 11:17 AM
with proper carbon dosing, a skimmer can remove nitrate and phosphate. But it is possible that they may not be removed in the proper ratio.

Organic carbon dosing increases the growth of heterotrphic bacteria which take up N and P.and may aid the growth of other organisms that take up N and P like sponges for example .These bacteria and their by products are then taken up by the skimmer. The ratio of N and P in the particular organisms taken by the skimmer may vary from the redfield raito, an en masse measure of C: N : P content in the sea.

While the organics fed by carbon dosing do take N an P with them and may not precisely balance at the 16N: 1 P en masse redfield ratio ,there is another reason for a potential imbalance from denitrification via anaerobic bacterial activity where NO3 is reduced to N with some of it forming N2 which bubbles out of the tank ; there is is no comparable exit for P.

I always liked wet-skimming, then adding salt to the replacement water, almost like a mini water change every day to bring the nutrients back into sync.


I also favor small water changes and wet skimming seems a good way to do it; however , the addition of new salt water won't add much if any nitrate or phosphate; it will add other major and minor elements from the salt mix, though.

If a nutrient deficiency in the tank is noted sourcing additional nitrogen or phosphorous via extra foods or direct additions of P or N like soidum nitrate or a phosphate additve are sometimes needed. Salt mixes genrally don't contain much if any N or P.

orcafood
11/17/2017, 02:34 PM
Yes but a water change will still dilute the ratio imbalance :) A real reef tank should have huge amounts of food going in and nutrients going out. I suppose I take that fact for granted. Thanks for putting some meat behind my ramblings, you make it sound much more eloquent.

bertoni
11/17/2017, 06:46 PM
I agree that the skimmer is only equivalent to a minuscule water change rate, if it is working properly. :) I was just being a bit obsessive.