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Re: surface scum

>Date: Thu, 19 Feb 1998 13:09:57 -0500 (EST)
>From: "Roger S. Miller" <rgrmill at rt66_com>
>
>On that basis, I'd expect surface scums to be fairly common in tanks that
>are less than a year or so old.  I also see scum appear in established
>tanks after something disturbs the microbiological conditions in the tank
>- - for instance, when the filter is changed, the substrate is disturbed or
>the fertilizer regimen is altered, and I expect that is normal.
>
>I don't think scum should be a persistent problem in an old tank under
>stable conditions - certainly it isn't a persistent problem in mine.

Other thoughts:

Someone long ago suggested that the surface scum is iron sensitive bacteria. It 
seems to start up when chelated iron mixtures are added.  [Or perhaps it's the 
EDTA left over after the iron is used by the plants?]

Can you correlate your scum experiences with iron or lack thereof? 

Re: stable tanks and scum

I would proclaim our 120g tank to be established and stable; Dupla regimen, two 
and a half years old, substrate heat, blah, blah, blah.  It has no visible 
surface scum due to a trickle filter skimmer box.   

However, late last year we set up a 29g rainbowfish grow out tank and plumbed it 
into the 120. It had a very thin layer of black gravel just to hide the bottom 
glass and a couple of Java Ferns attached to rocks for decoration.  An Eheim 
2213 pumped water out of the 29g into the 120g and a siphon tube returned water 
from the 120g to the 29g. The 29g had the benefit of the "good" water in the 
120g without the distraction of hungry mouths. 

Within a day of setting the 29g tank up, it's surface was thick with scum!  So 
from this I can conclude "It's in the water" and the skimmer box (or whatever 
means is used to "remove" the scum) merely keeps it from collecting into a 
visible mass. We added an Eheim Surface Extractor to the 29g and that kept its 
surface clear. 

So can folks corrrelate surface scum with iron additions; perhaps even with 
specific brands of fertilizer?  Do tanks using PMDD get it? 

George Booth in Ft. Collins, Colorado (booth at frii_com)
Need Info?  http://www.frii.com/~booth/AquaticConcepts.htm