Getting rid of that surface scum

[Plantbrain]

Well I tried it out, this weird idea of mine and it was night and day.
I cannot say it's true for every case but it is true for this case and many others I've played with over the years and I believe....that it can be generalized to one of the main primary causes for surface scum in planted tanks.

The idea:
General good plant growth produces clean surface waters. Lowering the CO2 level below optimal levels of 20ppm+ etc produced large amounts of surface scum layer. It seems that when plants are stressed for CO2, either from a temporary or also perhaps a chronic lowering of CO2, that they produce/leak out lipids and/or proteins.

The scum also dissipates quickly when CO2 levels are returned to 20+ppm and hence O2 levels are returned to that of a normal thriving planted tank.

Whether the production stops of the lipid/protein leakage from the plants or if the higher O2 levels dissolve the scum layer, I'm not certain.

But I can certainly correlated high CO2 with less surface scum.
Does anyone know of any analysis done of this scum layer in a planted tank?
It seems that the plants leak this scum out but it might be something else.
I forgot to mention that I formed a very thick layer of surface scum on the water, really thick by shutting the CO2 off.

After returning the CO2 to the tank at 30ppm, the surface scum that was there, is now gone after _a day or two_.

IME in the past, the scum layer often stays in a tank for a long period of time. This scum was completely gone with nothing done on my part except the CO2 adjustments.

A)It could be that the plants leak out some lipid etc at a relatively constant rate when CO2 stressed.

B)It could be some bacteria etc in the substrate are effected by the plant's growth rates or the roots of the plants leak something out.

C)It could be the high Dissolved oxygen levels cause the normal layer to dissipate much faster even when the plants are in good shape for CO2.
Say the plant had plenty of CO2, but no K+ etc.

I think A) is the most likely.
The other parameters have been left in good shape, no surface movement in the tank, surface skimmers etc.

Regards,
Tom Barr

[bclee]

That's a very interesting observation.

I would like to add my observation to see if it will help to shed more light on the mystery of the surface scum.

I have a 15gal tank with 36W PL + 15W FL. I maintain my CO2 >20ppm for most of the daylight hours. I usually have a thick film of scum on the water surface that I do not bother to remove.

Recently, for 3 weeks, I ran out of CO2. During this period, I turn off the 15W Fl and run my tank with only 36W PL. I also started dosing Seachem Excel. During these 3 weeks, I discovered that the surface film has reduced considerably that I could almost not see the film.

Now, I have return the tank back to the original condition. The surface scum has also returned.

3 things was changed:
1. Reduced lighting
2. No CO2 injection
3. Dosing of Seachem Excel

I was thinking that there could be 2 possibility. First, the film might be a by-product of photosynthesis and by reducing the lighting and no CO2, I get lesser photosynthesis and thereby, lesser surface scum. Next, it could be the Seachem Excel which was a photosynthesis intermediate has cause the plant to by-pass a certian photosynthetic step such that the by-product is not produced.

Well, I am a biochemistry dummy and I cannot substantiate my hypothesis. Just my 2 cents worth.

BC

[Plantbrain]

Try this:
Raise the CO2 up to 30ppm and make sure you have good nutrients in the tank. Do NOT do a water change.
My concern is that water changes remove the scum (at least for a day or two).

How long till you have another build up of scum on the surface AFTER a water change also?

Generally folks have a clean surface after water changes(lots of CO2 for the plants) due to removal of the scum and mixing etc.

Regards,
Tom Barr

[bclee]

Tried that. The CO2 is close to 30ppm. The scum return on day 2 after water change. It did not seem to be a marked change.

I will observe again on the next water change.

BC