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That Elusive Surface Scum


  1. QYNGA: Surface scum
    by George Booth <booth/> (Wed, 19 Nov 1997)
  2. QYNGA: Surface scum
    by Stephen Pushak <teban/> (Wed, 19 Nov 1997)
  3. Surface scum
    by mark.fisher/ (Wed, 19 Nov 97)
  4. RE: Surface scum
    by Charley Bay <charleyb/> (Tue, 25 Nov 1997)
  5. RE:Surface scum
    by Charley Bay <charleyb/> (Wed, 18 Feb 1998)
  6. Update re surface scum
    by "Frank I. Reiter" <FIR/> (Sun, 15 Feb 1998)

QYNGA: Surface scum

by George Booth <booth/>
Date: Wed, 19 Nov 1997

> Date: Tue, 18 Nov 1997 16:36:07 -0500
> From: "Frank I. Reiter" <>
> 1) What *is* this scum?

It has been reported as either a protein scum from fish food
(especially meaty foods like frozen cubes) or bacteria that seem to
like iron (from our dosing drops).  I'm not sure if I've ever seen a
definitive answer. This might be the same goop that collects in
saltwater tank protein skimmers. 

Anti-QYNGA: Protein skimmers don't work on freshwater tanks.  The
surface tension is too low.
> 2) What does it's presence tell me about my tank?

It says "your tank is just like my tank(s)".  All of our tanks have
had this surface film ever since

  1) we started raising plants

  b) we started adding CO2

  iii) we started fertilizing

All this was so long ago, I forget which might be the case <g> 

> 3) How can I encourage it to go away and stay away?

I don't think it will go away on its own unless you or someone else
figures out what causes it and changes that factor.  Maybe pH is a
clue (ours always has been close to 7.0).

Solutions to the problem:

Surface skimming, either with a trickle filter siphon box, an Eheim
Surface Extractor (fussy but effective) or some DIY device.

Laying a paper towel on the surface to absorb the film. Not a
permanent fix, obviously.

Heavy areation will break up the film and "hide it" with the obvious
drawbacks to a planted tank.  "Lack of CO2" if it wasn't obvious. 

I've always felt that the surface film is detrimental to gas exchange
so we always have something to deal with it.  All our tanks now have
trickle filter skimmer boxes but we've used the Eheim Surface
Extractors in the past on other tanks. 

OK, we put that sucker to rest.  

George "One down, 234 to go"

QYNGA: Surface scum

by Stephen Pushak <teban/>
Date: Wed, 19 Nov 1997

> From: "Frank I. Reiter" <>
> [snip]
> When the sum is thick I can agitate the water with my hand and it will
> break into small white bits.
> The questions then are:
> 1) What *is* this scum?

What we know so far about this stuff is that it is biological; it's some
kind of bacteria feeding off nutrients in the aquarium. I haven't seen
an identification beyond that on the APD. I have this intermittently on
my tanks.

> 2) What does it's presence tell me about my tank?

I get this most commonly when I have a tank with little or no surface
agitation. When there is a moderate surface flow as with a Whisper hang
on trickle style filter, the flow of water breaks the film up and it is
either eaten by the fish or drawn into the filter.  It has been
suggested that this is a kind of bacteria encouraged by the presence of
chelated iron in the water. It seems to occur under conditions even
where all nutrient concentrations are low or moderate. Low or high CO2
levels do not affect it; I've seen it on tanks with and without CO2.

> 3) How can I encourage it to go away and stay away?

Probably your best bet is to move and don't leave a forwarding address!
;-) Seriously though, I think the answer is in filtration. Either have a
filter which draws water from the surface as in an overflow style or
allow the return of an external filter to flow smoothly in a mild
waterfall fashion into the tank. To avoid excessive surface disturbance
and annoying trickling sounds, I glue a strip of thin plastic sheet onto
the outflow of my filter so that the water runs smoothly down it into
the tank. I suspect there is no effective way to eliminate the bacteria
themselves. At this time, we don't know what the bacteria is. It could
be introduced with fish, endemic in tap water or even airborne. I
suppose treatment with a UV sterilizing filter -might- be a possibility.
That's not very practical for most of us.

I think this QYNGA is because few of us have a definitive answer to
give. I look forward to reading what the others have to say about this
stuff. What's the technical term for it anyway? gunk? surface scum? ;-)


Surface scum

by mark.fisher/
Date: Wed, 19 Nov 97

     >One other thing, there are little (< 1mm) "fleas" that I can see
     >jumping on the scum patches. Could these little cretins be
     These insects are called springtails, of the order Collembola.  There 
     are several families.  They live on the water's surface, and probably 
     feed on the surface scum, along with plant debris.  A good general 
     reference on this topic is "Fresh-water Invertebrates of the United 
     States" by Robert W. Pennak.
     Surface scum is primarily composed of water-insoluble organic 
     compounds (proteins, fats, aromatics, etc) from fish food, and/or from 
     the decay of plant and animal matter in your aquarium.  As the scum is 
     both water-insoluble and lighter than water, it floats.  Secondarily, 
     other things can colonize the scum (presumably while feeding on it), 
     such as bacteria, fungi, and, of course, springtails.

RE: Surface scum

by Charley Bay <charleyb/>
Date: Tue, 25 Nov 1997

> "Frank I. Reiter" <> wrote:
> [snip, surface scum]
> > 2) What does it's presence tell me about my tank?

> George Booth <> responded:
> It says "your tank is just like my tank(s)".  All of our tanks have
> had this surface film ever since
>   1) we started raising plants
>   b) we started adding CO2
>   iii) we started fertilizing
> All this was so long ago, I forget which might be the case <g> 

I'm going to go out on a limb and speculate on two primary answers:
(1) greasy/fatty fish foods
(2) high nutrient/biological load that encourages relatively higher
bacteria populations.

I've been toying with my tanks quite a bit on the surface scum issue.
My 180g has a low fish load (20" fish, barbs/tetras) and no fertilization
or CO2.  I surface skim, and never have scum problems.  If I turn the
skimmer off (have absolutely no circulation or filtration whatsoever), 
I will develop a slight layer of scum over about a week if I'm feeding
fatty foods, like freeze-dried brine shrimp (it seems to be the worst).  
I'm probably a horrible master, but I've actually rotated a solid week 
of single-variety food just to see what builds up surface scum.  Some 
of the cichlid or community pellets or micro-pellets don't appear to 
generate any or as much surface scum after a week or more. (I'm
next going to move onto different brands).

Of course, I'm interviewing my fish regularly to see how they like
their diet and excercise regimen.  I have no mortality, though,
so I guess it's "adequate".

My guess is that the major factors are fish food type/volume, 
and many fish (with many slimy coats and much more biologically
active waste products).  For these experiments I've been working
with larger tanks and lower fish populations just to try food type
as it relates to scum production.  In writing this, though, I just 
realized I've done a bad thing by not measuring the quantities
and times I've added the food, though.  I will next move to constant 
food type and larger/smaller fish populations.  While I suppose plant
biomass volume may be a factor (plants do produce lipids and
fats of their own), I don't think it would be the lion's share (with
absolutely no data I'm guessing food and fish volume should
account for at least 80%).  

Over-fertilization, of course, would merely increase the range 
of biologically viable growth/reactions because you are moving 
ever-farther from a sterile or nutrient poor soup.  That would 
increase bacterial activity and surface scum, so I'm not fertilizing now.

> > 3) How can I encourage it to go away and stay away?

I agree with others that surface skimming is easiest, followed by
water changes or other mechanical control (I saw paper-toweling of
the surface here).  I've even let my tanks "sit" for a couple days
prior to a water change, let the scum settle on the surface, and
used my python to "skim" the surface water, all of which is removed
in the water change.  That seems to work really well for me.

Perhaps I will eventually be able to recommend specific food types
or fish volumes, but my guess is that the fish still need that food
variety and really fatty/greasy foods are probably very good for
them (so this is probably a pretty moot issue that we should
just live with).  I might end up giving them the equivalent of fried 
chicken in gravy 10% of the time instead of 50% of the time, though.

Isn't it *love* that lets me force them to eat more heathfully than I do?

As an aside, I'm thinking about starting to sample my tanks to
identify quantity/variety of active bacterial populations as it relates
to surface scum.  I work at a company that makes very expensive
instruments that sort cells, and we can just run the samples
through.  This "flow cytometry" is apparently in widespread use
analyzing zooplankton/phytoplankton or other critters in marine
systems... it seems like we freshwater guys should be able to use
it too.  You should *see* the amazing stuff they are doing with
yeast cells and ... beer.

- --charley

RE:Surface scum

by Charley Bay <charleyb/>
Date: Wed, 18 Feb 1998

Kin T Tam <> wrote:
> <snip> After removing that I've been
> getting surface scum.  The scum comes back very quickly.  It goes away
> after a large water change because of all the water movement at the
> surface.  But a day later a thin layer will start forming again.  I think
> the only way to deal with it is have a lot of water moving at the surface.

In my recent experiments with surface scum, also in large 
tanks (180g), I would turn off the pump for a day or two before
the water change.  I invert my siphon into a "U" in the tank, 
and thus skim the surface for the first half of the water change.
I can get most of the lipids, oils, or scum off the surface.
Then, the second half of the water change is to vacuum the
gravel (sometimes I don't do this part).

This seems quite effective.  It takes a while to bring the scum

- --charley

Update re surface scum

by "Frank I. Reiter" <FIR/>
Date: Sun, 15 Feb 1998

A few months ago I wrote about a problem I was having w/surface scum in one 
of two nearly identically setup 120 gallon tanks.  The only difference 
between them, aside from the species of plants/fish in them, was that the 
tank with surface scum was pH 6.8, the one without was pH 7.2.

For various reasons, the pH of these two tanks was reversed a few weeks 
ago.  Water was not moved between the tanks.  Within days, the previously 
scum-free tank that was changed to pH 6.8 developed a surface scum problem, 
while the other tank, which *had* had the problem, cleared up quite nicely.

I don't know what else may be a factor, but clearly pH makes quite a 

(Today both tanks are clear at 6.8 - The canister filters have been 
replaced with a trickle filter which draws surface water via siphon boxes.)

- -----
The very act of seeking sets something in motion to meet us;
something in the universe, or in the unconscious responds as if
to an invitation.  - Jean Shinoda Bolen

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