About filtration

>I'm interested in the idea of minimal filtration. What kind of filter
>system would be recommended by those who propose minimal filtration? On my
>20 gallon tank at work I have an Aquaclear 150 filter. The sponge in it
>catches dirt in the water but also acts as a biological filter by giving a
>home to the bacteria. What could one replace it with?
>in Vancouver which is very un-May-like right now.

I found that a simple powerhead with a foam sleeve does a good job of
mechanical filtration on my 125 gallon.  I have to clean it every 4
or 5 days, but it is easy to get at (unlike the Fluval cannister on
my 70 gallon).  As for biological filtering:  all you need for that
is water movement and surface area for bacteria to grow on.  The
plants themselves offer plenty of surface area,  so you don't need 
to worry about providing that.

in Boston, where it was 95 yesterday and 45 last night