phospholipids and pond scum


>According to my high-school biology
>class from way-back-when, cellular membranes (animals and bacteria) are
>primarily composed of phospholipids.  Cell walls (plants) are primarily
>composed of cellulose.

Here is a slight modification to whosever statement this was...animal and 
plant membranes are made of phospholipids..plants have an additional cell 
wall that covers it...but it doesn't make any difference whenthey are ground 
up into fish food.  Everything that is in the tank is make byproducts.. 
including stuff that is not very soluble in water, this is why we are doing 
water changes.  Surface skimmers will remove all of the floating scum very 
efficiently, but then somepoeple will say "but aren't you disturbing the 
surface of the water and removing too much CO2??"  Of course you are 
removing some of the CO@ that you just added, but if you are using the DIY 
CO2 set up, then what difference does it make anyway.  Just add more to keep 
the level where you want it. 

*** (in my opinion) *** I think that one of the big reasons that there is a 
problem with scum on the surface of the water is because we are not breaking 
the surface of the water in attempts to keep the dissolved CO2 levels high.  
If you look at the local pond you will see that the areas of the pond that 
are protected from the wind are also tending to get a nice layer of scum on 
the surface because the surface is not getting agitated and the scum is not 
getting "incorporated" into the water.  Personally i use cheap little 
whisper-type filters that hang on the back of the tank that over flow with a 
nice little waterfall when the water level drops due to evaporation.  I also 
and copious amounts of CO2 to the tank to make up for any that is lost.  My 
CO2 levels are always high, pH is fairly stable, and I have little problems.

One point that people tend to forget about pond scum is that it is 
preventing the light from reaching the plants.    

    John Davis (marooned in aggieland)
    Department of Biology
    jdavis at bio_tamu.edu
    jmd9261 at tam2000_tamu.edu