My new pond(2500 gallons) of three weeks has been saturated with pollen from the oak trees. The color of the water is now reddish brown. I'm doing water changes which is helping a little but I'm looking for another method. Someone told me activated charcoal in a net bag might help. Any suggestions?

Water changes and activated carbon will help. Buy a big box or bucket of activated carbon. Put it into a mesh bag. They sell mesh filter bags at many aquarium stores. The holes have to be small enough to keep in the carbon. Rinse it well and don't breathe in the carbon dust. Then, put that in the pond near moving water, usually in the filter. Depending on how much organics are in the water including from the pollen, you may need to change the carbon in a few days or a week and put in more if the water's still discolored. I also suggest testing your pond's pH to be sure that the pollen or other things haven't lowered the pH. Good luck!