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Re: Surface scum

>hmmmmm.... it's been my (limited) experience that surface scum is
>directly related with surface agitation. if you're running a wet/dry
>filter with an overflow collector you won't have any surface buildup.
>if you're running a canister filter and trying very hard to minimize
>surface disturbance to reduce CO2 depletion then you're going to get a
>solid surface.

On my 29G I run a fluval 303 with the spray bar located well below the 
surface (to prevent agitation) and also an aquaclear power head for 
additional water movement.  The powerhead is also oriented such that it 
does not disturb the surface much.  I don't have a surface film at all on 
this tank.

I used to get a solid white slimy film over this tank.  I didn't really 
care about it too much, but I've noticed that it's gone.   The biggest 
change that I've made recently is to add sodium bicarb to this tank to 
raise the alkilinity and the pH.  I use yeast CO2 injected into the 
canister input, and the pH used to be around 6.4-6.6, with an alkilinity 
(kH) of <2deg.   After I added sodium bicard, the alkilinity increased to 
4-5 degrees, and the pH inched up over 7.0.  This supports someone's 
observation that the surface scum is only present when the pH is less 
than 7.

This is not to say that you can't get rid of surface film by using 
agitation or a skimmer box, but my tank is evidence that you can have 
zero surface movement and zero surface film.  pH could be the key.

Now, I also recently added some Jobe's plant sticks to the substrate 
(13-4-5 formula - couldn't find the fern and palm variety around here) 
and I'm pretty sure my phosphate levels are high.  I don't have a test 
kit for this, but the filamentous algea is much more prevalent than it 
was before.  So maybe there's another factor contributing to the 
dissappearance of the surface film.

Just my observations, FWIW.

in Ann Arbor, where we haven't had snow for at least a month. 

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     `/  \        ,/'  Steve Robertson, Research Fellow
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