If you are interested in putting fish in your homemade fountain or pond, you will have to make sure the water is purified.  Chlorine is an additive that is used to neutralize the contaminants in drinking water, however it is not good for fish.  Dechlorinators are available to get rid of the chlorine and there are chemicals that can adjust the ph. 

There is a difference between koi and goldfish.

Koi are more expensive and require more commitment from the gardener because they can grow up to two feet long and live up to one hundred and seventy-five years.  Koi require a high level of water quality.  They like to eat plants and to root around them, which can make the water murky. 

Goldfish are very easy to deal with and they do not eat plants.  They are also very colorful and if you are a plant lover then goldfish are your best choice. 

Both koi and goldfish need to be fed about once a day and it is a good idea to feed them at the same time every day.  Avoid overcrowding your pond.  You should have a balance of aquatic life including plants, fish, and scavengers can help control algae and maintain water quality. 

Before adding goldfish to the pond, you need to acclimate them.  Add some of the pond water to the goldfish bag to help them adjust.  Let it set for twenty minutes.  While the fish are being acclimated, add the plants.  You can put some bricks in to give height.  Add a floating plant to give fish something to hide under and to help cool the water. 

The best thing to maintain your pond is to keep it clean.  A hand skimmer is good for getting out unwanted debris from the pond.  Keep the water moving.  This will add oxygen to the water and helps prevent mosquitoes from laying eggs.