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QYNGA: Surface Scum

>Date: Tue, 18 Nov 1997 16:36:07 -0500
>From: "Frank I. Reiter" <FIR at istar_ca>
>Early this summer I setup two 120 gallon aquariums each w/2 175W MH
> *One* of them has had a persistent problem with surface scum, which comes 
>and goes not apparently in response to anything I am doing.  The problem 
>tank is ~ pH 6.6, the other ~7.2 - aside from that there are no
>that I  can see making a difference.  (different plant and fish choices, 
>but similar amounts of both in each tank.)
>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?
>2) What does it's presence tell me about my tank?
>3) How can I encourage it to go away and stay away?
>(I am soon installing a trickle filter with siphon boxes on those two
>and expect that the drawing of surface water into the filter will answer 
>#3, but I am still very curious about #s 1 and 2.)
>- -----

This question was addressed at length way back when on rec.aquaria before
the re-org, but that was years ago.

Surface scum is usually a protein buildup on the surface of the water.
Setting up your trickle filter with a surface skimmer will probably move it
to the sump, where you won't have to look at it.  Airstones work too, but
they tend to splash the scum against the sides of your tank and the canopy,
resulting in a crusty build-up.

I find that surface scum usually coincides with a fairly high fish load in
the tank, leading to lots of feeding.  When I run a tank where I don't feed
much, I never have surface scum, even if I don't have a surface skimmer
operating on my filtration system.

I've also read that surface scum can be a bacterial bloom indicator of high
iron levels.

Off-topic, but Just for the record:  Slimy bacterial buildup on CO2
reactors is normal if you're using yeast to generate CO2.

David W. Webb
FishRoom staff member who is still a regular.