Hi all, I'm one of the occasional lurkers - it helps me maintain my pond
scum aquarium for winter microscopy. Thanks for all the help. =)

Anyway, here's my obligatory wierd question - if I wanted to go to the
local lake, and hang a hose down into the water and pump small quantities
though a filter paper and back into the lake for ten minutes or so... are
there small pumps that could pump water like this up against a filter (high
resistance, should probably be considered 'clogged')?

I guess such a pump would have to somehow avoid building up a lot of
pressure, maybe let water slip back though to avoid popping the filter
paper? Being able to adjust the pressure it produces would be ideal. And
it needs to not "chop up" the water - so obviously I am way out of my league
here.

When I do this in the lab, the filter only lets though about 100ml a
minute. It's a 4" circle of paper, supported on a surface full of holes at
the bottom of a fancy ceramic funnel, and vacuum pulls the water through.
After awhile, the paper turns green, and holds lots of nifty little
microscopic life - of the open-water variety.

I can build the filter bit, but need suggestions as to pump technology.
Are there little fountain pumps like this, for example? Any help
appreciated! -cmb

p.s. - Happy Thanksgiving!