White growth on CO2 exit

A little while ago Stephen and Greg were talking about eliminating the
white fuzzy stuff that appears out of nowhere around the CO2 producing
tube. Well I just had an interesting thing happen re this stuff.

In my tank at work, a 20 gallon, I am running my CO2 into an upturned half
plastic bottle where I let it sit diffusing. It's been going about four
weeks now and up until yesterday the white stuff was growing prolifically
-- it had filled up about an inch worth of the bottle.

Well, yesterday I noticed that two of my guppies and one of the platties
were up inside the CO2 catch bottle tugging on and appearing to eat the
white stuff. Today, when I arrived at work, I saw that it was all gone! So
apparently fish like to eat it. If it's available to them I suppose the
fish would clean it up for you.

BTW does anyone know what this is? Some form of protien? Plant life as in
fungus, mold?

in lovely sunny Vancouver