You will need to start using bacteria/aeration. You shouldn't use any copper as it is very toxic to Koi. Use GreenClean or Phychomycin which is an oxidizer that kills algae.This product is labeled as an algaecide for use in lakes, ponds and aquaculture. Blue-green algae is the primary target species, but may be used for ither types of algae according to labeled rates. Dosage rates range from 3 lbs to 16.9 lbs per acre-foot of water for control of nuisance algae.