Remove fish first from a garden pond
Unplug the pond pump and remove any fish using a net, placing them in a large tub. Fill tub first with water from the pond before it has been cleaned. Place an inexpensive aerator or small pond pump in the bucket to oxygenate the water while the koi pond cleaning is under way. If the water garden pond is small and cleaning can be accomplished in a few hours, gold fish will generally survive without an aerator. Keep the tub in the shade.