Still green....

I've written for suggestions before, and have tried them all...but, I STILL
have a nasty, green pond. I had clear water for 1 week since spring. I'm
really discouraged and do not know what to do. I had that "floating" algae for
over a month, that has stopped, but I still can't see my fish. Plenty of
plants, although they are not doing half as well as they did last year.
Bio-filter (85 gallon) which is just full of green, gummy, slimy crap
constantly. I think I might be defeating my own purpose - have been rinsing
out filter and media weekly - it gets that gummed up. Last year we only
cleaned once.

History: 2nd summer for pond.
SIze 14'x12'
Gallons: appx. 4200
Depth: 2 1/2 - 4' deep
Fish 3 koi 6-7"
2 koi 3"
Baby comets (maybe 40) from last year - (their mommies eaten by
the heron)
Waterfall and spitter
Full sun
Thanks for any ideas, suggestions. I didn't want to add chemicals to the pond,
but I'm ready too now. What works? I have been using BZT, no help, no change.
Thanks, Cathy