Greenish Tint!

I would appreciate advice on how to eliminate the green tint in my pond
water. The water is "clear" in the sense that I can see the bottom but the
green tint, which I assume is algae related, is not good.

My system consists of the following:
- A 4000 gallon concrete pond (with black epoxy coating) ranging in depth
from 3 to 4 feet. We currently have about 15 large koi plus many fingerlings
from recent spawns.
- A re-circulation system that includes a 36 watt UV light and a large
Cyprio filter (18 brushes and 12 foam filter blocks). I clean the brushes
and foam blocks each week.
- The pond is in full sun much of the afternoon; but, about 35% of the
surface is covered by waterlilies.
- I treat the pond water according to the directions with "BZT Aquaculture"
which is a brand of "microencapsulated bacteria & enzymes."
George