Part Shade under Fir Tree

Hi. I'm an experienced "ponder" for full sunlight location. Small ponds
connected by waterfall, works fine, minimal algae problems. Now I want to
make a bigger one, about 24 deep by 6' wide by 9' long. Yeah, I know, big
only by my standards. It will be a water garden with gold fish, no Koi. It
will have partial shade, full sun only about 4 hours/day. I'll keep an
oxygenating clear surface space by using a livestock floating tank heater.
Have used that last fgew years and has worked well.

My biggest questions are what to expect from reduced sunlight (as compared
to full sun), and what to expect from dropping needles and cones.

Walt in Iowa