Before your add goldfish or koi to your water garden, follow these tips:
Introduce fish gradually. Float plastic bags containing fish on the water for 30 minutes to equalize temperature. Then, open the bag and let pond water come into the bag before releasing fish.
Do not overstock. The rule of thumb for stocking goldfish or koi is 1 to 2 inches of fish for every square foot of pond. Your fish will be stressed by crowded conditions.
Do not over-feed fish. They eat small amounts at a time, and the rest sinks to the bottom of the pond and pollutes it. Keep in mind that fish will also feed on the roots of plants as well as mosquito larvae—which keeps the bug population down.