does heavy skimming remove PO4 and/or NO3?

[Dan_P]

Originally Posted by tmz

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]

Originally Posted by Dan_P

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]

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]

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]

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]

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.