Water Turned Green Algae in new pond......Help!

I have a pond I just got started about 6 weeks ago. It's 5' x 8' and
22" deep at the deepest point. I calculated it to be around 450
gallons. I have 5 Goldfish and 3 Koi in the pond. So far I only have 1
Iris plant. I'm running a 750 gph pump with fountain and a waterfall.
My water is turning very green and murkey. I can only see about 6"
deep into the water. The pond get's sun most of the day. I feed my
fish 2 times a day with shrimp pellets. I've tried Accu-clear and it
only seems to have gotten worse. I put a clean filter near my
waterfall to filter it before it drops into the pond. In 1 hour the
filter turned dark green. Do I need to do water changes? Will this
green water harm my fish? Any suggestions about how to get rid of this
green algae?

Thanks in advance