Do you have a bottom drain in your ponds?
What about veggie filter?

no bottom drain...wish I did, but it wouldn't work in the goldfish/lily
pond....it would work real good in koi pond. My ONLY method of filtration
for my ponds are veggie filters...wouldn't ever have a mechanical filter. I
love the veggie filters. Jerri

http://www.fringeweb.com/Ponds/JerrisPond