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[APD] Re: Scum layer

> Very interesting, Tom.
> Since you promoted the scum by "removing" CO2, could it be
> that the scum you got was CO2 sensitive but that that is
> not always the case with scums?
> curiously,
> Scott H.

I doubt it. It's possible but I'll look at the obvious first.

It responds well to good plant growth more than just high CO2 or high O2.

If we assume plant growth idling when CO2 levels drop, this is the likely
source of the scum production.

I'm looking at where this scum likely to come from, the source of this scum
first.... then I'll move on to decomposition. It's good to know where you
are coming from in order to know where you are going.

Leakage vs decomposition are mediated differently.
Leakage can occur when the plant has too much of something, say NO3, PO4
etc, and this would build up when there is not enough carbon to make the
skeletons for sugars. Many algae leak like crazy. Some lose 50% of what they
fix and make. Some are real misers. But misers when? And with what?
If CO2 is limiting, wasting something other than Carbon is likely to occur.
The plant(or algae) will hang on to the limiting nutrient as best it can.
While some slight acid addition in the form of CO2 occurs (mild reducing
agent), high O2 levels are going to be more destructive to many organic
compounds(O2 being pretty strong oxidizer) vs the CO2. Reduction would have
to be fairly intense to have the same effects as this highly oxidizing water
column. But even without the plants producing O2 + us adding CO2, the plants
by themselves seem a more likely candidate for the production/reduction of
this scum. I might be wrong, I don't know what chemical compounds are in the
scums. They might be inactivated/destroyed by slight reducing agents such as
high CO2 levels.
 Proteins are made from amino acids. Lipids are highly reduced forms of
carbon. The strong oxidation of O2 should have a greater effect on these
than CO2.   

 I have Gas O2 as well as CO2 to compare this too also. The scums were
primarily dust, some algal scums in those tanks but the effects of the O2 vs
CO2 high level tanks was not effected as I recall. All the tanks seem
similar with respect to surface scum formation.

The most plausible way this much scum could be formed is from plant
leachate. So what causes a plant to leak more? Deprive it of CO2 first.

But does this apply to long term plants adapted to low CO2 levels? I don't
think the wastefulness of the plants last that long. I think that perhaps
after a few weeks, they adjust to the new conditions. But during that time
or folks have high CO2, then low(too low) CO2 levels and have gas/DIY etc
varying a lot, they will likely get this scum.

But, I would urge anyone that does indeed have scum of the surface to up the
CO2 and make sure it's high(20-30ppm) for the whole day length.
Make sure the NO3, PO4, K, Traces are added and see if it removes the scum.

I believe some inadequate CO2 systems that has the the concentration of CO2
up and down frequently might contribute to surface scum.



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