Surface Skimming Thoughts

[Azureef]

I have gotten back into saltwater recently and have a 55 up with LR only so far. I do not have a sump (yet?) and thus with a HOB skimmer I have no surface skimmer.

Tonight, as I sat and looked at the thin film that occurs naturally and pondered it a thought occurred.

Why do we skim this back into the water column vs. removing it?

Why don't we remove it from the system instead of mixing it up into the water column?

No doubt, once the overflow system is employed to "skim" this unwanted material, it is never seen at is merely mixed into the water column.

Then, one relies upon a protein skimmer and various other filtration methods to remove that unwanted material which would float on the surface if we did not use this type of system.

As it would seem there might be a quicker way to remove the material, I wondered... is hiding that surface material immediately by mixing it into the water column the best way to handle it?

As is such, with my non surface skimmer system (for now) I decided to use a small receptacle to skip that surface film completely out of my system instead of adding it to the water column.

I realize that there are other reasons for using a sump system... but is mixing the material that floats to the surface back into the water column really the best thing to do?

(perhaps the sump could be closed for a time, and allow a closed loop in the sump to allow for life and anything needing moving water to continue, while particulates are allowed to gather at the surface, and then completely removed from the system vs mixing them into the water column)

The next question is, does that film contain enough bad mater to warrant instant removal vs mixing?

All ideas, knowledge, and thoughts about the subject (links to scientific data concerning surface film) are welcome.

Good to be back btw.

 

[lancer99]

I've had a few systems that didn't have surface skimming, and have used mechanical means (either pieces of paper towelling, carefully laid across the surface, or the same method as you), but the surface layer comes back after a few days, and it's just another maintenance chore that quickly becomes boring.

My assumption with surface skimming is that the organics that make up the surface layer are in a relatively high concentration once they reach the skimmer, and since they're obviously bipolar, are removed fairly quickly. So although some may make it through the skimmer and back into the tank, the combination of relatively high rate of removal + the fact that it's a continuous process, means that a surface film never gets to form.

I think the proof is in the pudding....I've never seen a (properly adjusted) surface-skimmed tank that had that nasty layer on the top.

Depending on your HOB skimmer, you may be able to get a surface-skimming box for it.

Welcome back!

-R

 

[TBartkus]

> Why do we skim this back into the water column vs. removing it?
> Why don't we remove it from the system instead of mixing it up into the water column?

Why indeed! Many of us do remove it.

> Then, one relies upon a protein skimmer and various other filtration methods to remove that
> unwanted material which would float on the surface if we did not use this type of system.

I believe it is common practice to take the surface water, "skin" and all, and feed that directly to a skimmer. A skimmer being a filter particularly effective at removing precisely that "stuff" that sticks to the air/water interface.

Blessed are those with a sump. I don't have one. But I do use an overflow box and my skimmer draws from inside overflow box. All the water the skimmer sees comes from directly off the surface, skin and all.

And the surface is crystal clear ;-)
-Tom

 

[BennyFrank]

No sump here either and I do occasionally battle with surface scum. I've heard a lot of it may be due to oils that come off of frozen foods. I've started "pre-washing" my foods and I think the scum has subsided somewhat.

Has anyone used one of these or something similar?

http://www.fosterandsmithaquatics.com/product/prod_display.cfm?c=3578+3579+12703&pcatid=12703

 

[smatter]

I use a Tunze Nano Cleaner to skim my surface, but it is mainly for chem and mech. I don't really need it, two Streams pointed at the suface mitigate any film which is quickly removed by the skimmer.

 

[wooden_reefer]

I have gotten back into saltwater recently and have a 55 up with LR only so far. I do not have a sump (yet?) and thus with a HOB skimmer I have no surface skimmer.

Tonight, as I sat and looked at the thin film that occurs naturally and pondered it a thought occurred.

Why do we skim this back into the water column vs. removing it?

Why don't we remove it from the system instead of mixing it up into the water column?

No doubt, once the overflow system is employed to "skim" this unwanted material, it is never seen at is merely mixed into the water column.

Then, one relies upon a protein skimmer and various other filtration methods to remove that unwanted material which would float on the surface if we did not use this type of system.

Skimming the surface is basically a gaseous exhange issue. You promote gaseous exchange by breaking the surface film. It would be better to remove the surface film, but how?

Skimming the bulk water with a protein skimmer is basically a water chemical quality issue, (other than dissolved O2 as a "chemical".)

 

[Azureef]

Thanks for the response. Still learning.

"Organic compounds which are attracted to air-water interfaces will form in your reef tank."

.....and

"These will show up as an oily film on the water surface. "

that is with a system that does not have a "surface skimmer".

I am looking for any scientific test results that offer the film contains.. many results for "protein" (hence the old name protein skimmer" and many results for "organic compounds". Nothing yet found regarding the amount of "organic compounds" measurements in the film.

As freshwater is not able to use a protein skimmer aka foam fractionator there are many articles on removing the film that contains the organic compounds via such means as simple as paper towels or a container used to skim the surface and that water discarded vs mixing it *back* into the water column.

I have some hesitancy believing that if skimmed directly from the surface and sent directly to the protein skimmer, that no organic compounds escape the protein skimmer.

I am not an advocate of going with out a sump and will add one soon.

Its just at this pause, I wonder if removing that film in 5 mins is faster than trying to remove those compounds by mixing them back into the water column.

Additionally an idea is to skim that surface film (once allowed to form) via scheduled water change.

Of course there is no film seen with skimming, but that does not mean the compounds are gone. Yes it cannot be allowed as it has an adverse effect to gaseous exchange. Just bouncing the how to remove it around a bit.

Does anyone have a link to any studies on exactly what has been found in the film?

Thanks

 

[TBartkus]

> I have some hesitancy believing that if skimmed directly from the surface and sent directly
> to the protein skimmer, that no organic compounds escape the protein skimmer.

I don't think anyone would tell you "no organic compounds escape the protein skimmer."
I would tell you, however, that the visible surface film is gone. The surface is sparkling clear.

A skimmer is especially effective at removing precisely that stuff that does form a surface film. I do not believe that would include all possible organics in the water.

Large organic molecules are not generally very soluble. They tend to stick to surfaces with the water/air surface being one such sticking place that is both obvious and objectionable to the hobbyist admiring his handiwork.

Large organic molecules decompose into smaller molecules that are more soluble. The idea behind a skimmer is to short circuit that process by getting the big (protein) molecules before the break down and become harder to catch. That tendency to stick to the air/water interface is the very property that the skimmer exploits to do it's work and it is quite effective.

> Yes it cannot be allowed as it has an adverse effect to gaseous exchange.

Gaseous exchange AND the bright lights we try to project into our tanks!
But tipping the surface water into an effect skimmer has those two problems eliminated. Completely!

> ... but that does not mean the compounds are gone.

So the surface film is gone but you are still worried about organics the skimmer missed. As well you might! It won't capture everything but I would urge you to consider it as the very first line of defense!

An effective skimmer eliminates much of the large molecule organics before they break down into smaller, more soluble and therefore more troublesome "stuff". But not all of course.
Your next line of defense is an excellent grade of activated carbon.

I didn't even mention regular water changes. I hope I didn't need to ;-)

> Does anyone have a link to any studies on exactly what has been found in the film?

Not I. But I would be surprised if someone hasn't analyzed and written about the smelly yellow gunk that appears in the skimmer's waste cup.

That is where the surface film went now that you have removed it!
-Tom

 

[FMarini]

Actually there are two very important articles by Ken Feldman on what exactly a skimmer removes from the water, (what is the composition of skimate) and how effective skimmers are. The articles are on another site. here is a sneak peak

In summary, the skimmer is pulling out a solid, water-insoluble mixture of compounds that consist by weight of (approximately):
44 % of CaCO3
5% of MgCO3
11% of biogenic opal
34% of organic material
0.5% of phosphate

I think you guys will be surprised(to say the least) to see what it really doesnt do and how effective these devices are (or arent).

google search Ken's name and skimmer skimate to review

 

[TBartkus]

The article is available: http://www.advancedaquarist.com/2010/2/aafeature
And it is worthy!.

> I think you guys will be surprised(to say the least) to see what it really doesnt do and
> how effective these devices are (or arent).

Very interested, but not necessarily surprised.
It takes some careful reading though!

>> 1.99 % by weight Mg implies that the total amount of Mg in the 5.18 gm sample
>> is 103 mg. Assuming that all of this Mg is in the form of magnesium carbonate ( .....

That "assuming" needs some careful consideration.
The author isn't even suggesting that Magnesium carbonate is being selective removed by the skimmer. He is simply using Magnesium Carbonate as an accounting trick to express the rather ephemeral notion of Magnesium ion present in the skimmate. What he doesn't know, can't know, and indeed discusses why he can't know is how much of that Magnesium was bound to big organic molecules. Ditto concerning the calcium carbonate levels you quote.

The figure of 34% (of skimmate!) tells me skimming is an extremely effective at organic export.
But the "slam dunk" - "using a skimmer is a *great* idea" for me was was the phosphate export. If you feed, you introduce organic phosphate. If you skim, you export organic phosphate before it breaks down into the kind of phosphate hair algae will really appreciate ;-)

Concerned about organics building up in your reef tank?
You really, *really* do want an effective skimmer.

Skimmer + activated carbon + water changes = Zero organic buildup in your tank.
-Tom

 

[FMarini]

Hi tom--
glad to read you weren't surprised. Most folks mythically believe that skimmers are very effective- they are not.
Infact Ken's first article (Jan 2009) suggests that pretty much (all) skimmers(that were tested) are capable at removing only about 20-35% of organic waste from the water, it didnt matter if its was an inexpensive skimmer, or a super duper expensive skimmer(althou bubble king was the most efficient). Some were faster than others-but 30-35% seems like the top end

Next, i read the data from article 2 differently than you. What it tell me it that water changes + carbon is more effective than skimming.
quote"None of the skimmers tested removed more than 35% of the extant TOC, leading to the conclusion that bubbles are really not a very effective medium for organic nutrient removal"

I didnt link the article because usually RC doesnt allow links to competing websites, but thanks for that

 

[TBartkus]

> glad to read you weren't surprised. Most folks mythically believe that skimmers are very
> effective- they are not.

Ahhh! But I do believe skimming to be very effective.

I've run a variety of tanks over many years without. Just a good carbon and water changes.
Ever hear of "old tank syndrome" ? That's the situation I always ran into.
The tank would run pristine for 6, 8, even 12 months then wham - hair algae all over the place.

This was always phosphate related. Water changes don't help. Turbo snails don't help. Mechanical removal is an exercise in futility. Not enough $$ for the buckets of phosphate remover needed.

BUT add an effective skimmer !

Just watch the phosphate decline and the hair algae die off. Even under bright halide lights the hair algae dies away. Never again will I run without a skimmer.

Just look at and smell the gunk in the collection cup. That was in your water and now it's not.
I don't think there are many who would argue against the effectiveness of skimming after that.
-Tom

 

[wooden_reefer]

Hi tom--
glad to read you weren't surprised. Most folks mythically believe that skimmers are very effective- they are not.
Infact Ken's first article (Jan 2009) suggests that pretty much (all) skimmers(that were tested) are capable at removing only about 20-35% of organic waste from the water, it didnt matter if its was an inexpensive skimmer, or a super duper expensive skimmer(althou bubble king was the most efficient). Some were faster than others-but 30-35% seems like the top end

Next, i read the data from article 2 differently than you. What it tell me it that water changes + carbon is more effective than skimming.
quote"None of the skimmers tested removed more than 35% of the extant TOC, leading to the conclusion that bubbles are really not a very effective medium for organic nutrient removal"

I didnt link the article because usually RC doesnt allow links to competing websites, but thanks for that

30% is not a lot?

It depends on the original expectation.

 

[Azureef]

Great reading the responses.

As I continue to follow the thread I would like to throw in 2 sources regarding the subject.

1. Organic Compounds in the Reef Aquarium - Randy Holmes-Farley

Organic materials represent what is likely the least understood area of chemistry in reef aquaria. This fact is not especially surprising as they also represent a very poorly understood aspect of chemical oceanography. . . .

DOM and POM Export Methods

There are a variety of ways to export organics from reef aquaria. These include the use of activated carbon, skimming, polymer resins, and mechanical filtration, and may also include the carbon and sulfur denitrators.

that is from http://reefkeeping.com/issues/2004-10/rhf/index.php

2. SML - Sea surface microlayer -

The sea surface microlayer (SML) is the top 1000 micrometers of the ocean surface. It is the boundary layer where all exchange occurs between the atmosphere and the ocean [1]. The chemical, physical, and biological properties of the SML differ greatly from the sub-surface water just a few centimeters beneath [18].

Organic compounds such as amino acids, carbohydrates, fatty acids, and phenols are highly enriched in the SML interface. Most of these come from biota in the sub-surface waters, which decay and become transported to the surface [17]; [19], though other sources exist also such as atmospheric deposition, coastal runoff, and anthropogenic nutrification [1]. The relative concentration of these compounds is dependent on the nutrient sources as well as climate conditions such as wind speed and precipitation [19]. These organic compounds on the surface create a "film," referred to as a "slick" when visible [18], which affects the physical and optical properties of the interface. These films occur because of the hydrophobic tendencies of many organic compounds, which causes them to protrude into the air-interface [1]; [20]

from: Wikipedia http://en.wikipedia.org/wiki/Sea_surface_microlayer

Also fwiw

The skin of the sea is only centimetres thick, but because it covers 71% of the surface of the planet, it is the largest single ecosystem.

The thin layer of oily material on the surface of the sea is an important part of the water cycle as it helps control the rate of evaporation. It is also a highly nutritious food source for many species of microscopic plants and animals called Plankton. On calm days we say the sea is "slick calm" or "oily calm" because the microscopic layer of oil is evenly distributed on the surface.

From: A bubble absorption device for the isolation of surface-active organic matter in seawater.

The primary mechanism by which geochemical species are transported upward across the boundary between the ocean and the atmosphere is associated with the production of aerosol particles which is, in turn, the result of bubbles bursting at the sea surface

Most articles I have read concerning the removal of organic compounds mirror Randy Holmes-Farley's method. I would not mix in a teaspoon of organic compounds into my water, thus I am still interested in other removal methods that would not use mixing them back into the water column. This may not be effective at this time ie. using a 1 dollar plastic receptacle to remove the film thus requiring other equipment to be taken out of the loop temporarily. It is interesting to ponder nonetheless.

 

[wooden_reefer]

Surface skimming and "protein skimming" are often somewhat related.

If your open loop flow is slow and/or a significant portion of the return water into the sump is from skimming the surface, the organics concentration in the sump may be a little higher than in the main.