Need Koi assistance 911

I am pretty new to this whole pond thing but have managed to keep 6
large koi (one is about 3 lbs!) and several goldfish alive and spawning
baby koi and goldfish all summer in a 1500 gal pond. Until today.
Yesterday, I was topping off my pond and left the water running
accidently for about 2 hours, the pond overflowed and I am afraid some
insecticide I had on plants usually far away from the pond and in pots
seeped into the water as it receeded back into the pond as the pump
worked to correct the overflow. This morning all of my white and
orange (all about 6-8 inches long) and 2 large goldfish were floating.
There is a slight film on the top of the water which I scooped out as
much of the top of the water I could. All the other fish seem
lethargic and are coming to the top to get air producing bubbles. It
is rather chilly in Oklahoma this morning and the water is probably
about 40 degrees. Are my fish lethargic because of the coldness of the
water and getting ready for winter? Have I saved the ones that made it
through the night, or should I expect all of my fish it die off one or
two at a time? I am sure they got some poison in their water from the
plants overflowing into the pond, I just don't know how much. Could it
be the water has been too cold since the temprature in the air has been
45-50 dgrees in the morning for the last few weeks and I have been
feeding them as usual not knowig how to feed koi in the fall (I do
now). Usually just the vibration of someone waking across the patio
makes all 30 fish come to the edge and beg for food, now they are
pretty lazy looking. Please, someone help me... do I need to empty the
pond down to 25% and refill, or let the pump and filter do the work?
Did I poison them or did they die from overeating in cold wet weather?
Please email me a copy of your reply since I am also new to blogging
and am not sure how to check for replies.
Thanks!!