I put in a pond a couple of weeks ago, and it looked great. It is 380 gallons and has a pump that circulates 400 gallons per hour through some filter media. My problem is the pond is in a area with some oak trees and I skim out the leaves and debris but the water is now so dark I cannot see the bottom (28" deep). Do I need to put charcoal in the filter? Or What? Thanks in advance for the advice. Glenn