Well, the biomass is a huge difference........even if you treat the tanks the same........then there are plant species differences...................then flow rate differences between filters...........many things are different between tanks.
This makes trying to figure things out difficult without really isolating things to very simple systems.
Many aquarist make this mistake, they assume that the tanks are relatively similar........
But adding a much higher level of complexity just with 2-3 variables becomes very daunting, adding, 10-20 variables turns the brain and the model to mush.........
I think it's best to isolate the 10-20 things one at time in isolation, then try and synthesize them together.
It is better to know a lot about one thing than little about many things.
It's hard adding every factor together.
However, and neat little trick, one I employ: Try and induce the surface scum.
Or try and induce algae by adding "Excess" NO3, light, CO2, PO4, NH4 etc........
You must try and experiment with ecological questions, not just watch and observe alone.
Those days are long over in Ecology as a rule, it is far more experimental these days. Physiology and molecular methods have long employed such methods to try and induce something.
Problem is...........few aquarist are really willing to try and make algae blooms, surface scum, stunt plants, kill fish and shrimp etc........
They just want to know how to prevent it, not kill it, or set up experiments to answer such questions.
This represents a huge gap between learning more and getting very far answering such questions.
I do some..........but I'm human also, and can only do so much.
Also, while CO2 reduction induced it in several tanks, I've also been unable to induce it others.
I speculate organic materials may have been the source of the proteins and lipids(hydrophobic organic compounds).
However, these are much more rapidly oxidized and broken down when the bacteria have plenty of O2(via plants, or H2O2, or pure O2 gas).
So that explains why poor CO2 might induce it(less O2) and adding more CO2 removed it.
So rather than CO2 alone, perhaps good bacterial cycling seems key, although many seem to ignore it and some suggest foregoing all filtration, something I've not found none too wise.
Again, such a hypothesis can be tested by aquarist.
No need to have a lab etc.
I had issues with a smaller canister on a large tank. It had a lot of scum. I added more CO2, the issue went away.
I am curious that if there was a larger higher flow canister, or if there was a wet/dry filter etc, that the system would be much less prone to this scum layer?
More/less CO2 might be just a secondary affect.
Organic material/waste might be much more the issue than plants leaching with varying CO2 dosing.
I did induce algae with left over plant leaves that where pruned from another tank. So old leaves can induce some issues, I do not recall if there scum layer was formed with that though.
Right now:
I have a small 20 gallon tank with a tiny filter, it has a nice scum layer.
I also have a large canister on another tank, similar light/CO2, biomass etc.
No scum ever, both are in the same room, open top , high light(450 micromols), lots of CO2.
So come to think of it, CO2 alone in that tank(there are no fish/shrimp etc) cannot be the only factor, the CO2 is pretty high!
But the filter is very different.
I do have another large filter I'd planned to add, so it'd be interesting to see if it cleared it up.
Also, H2O2. Or Pure O2, which I do have.
Regards,
Tom Barr
