I'm trying to get a pond going with 1/2 barrel that was used for red
wine. I'm not using a liner, and I've filled it with water and some
plants (water lily, hyacinth, anacharis, a couple of marginals). The
problem is that after about a week the water turns really foul: it gets
this white filamentous stuff in it and a really nasty sulfurous smell.
I've tried emptying and refilling, but the same thing happens each
time. Also, I've noticed these little critters, about the size of a
grain of rice, with an equal sized pointy appendage wriggling around in
there. They don't appear to be mosquitoes.

Any advice would be greatly appreciated.