Chances are … if you have a pond, you have fish. In fact, your pond fish might be the primary reason why you even wanted a water garden in your yard. Fish are fun to watch and most pond owners name each and every one of their finned friends. While fish create a memorable experience, they can also bring headaches to water quality if you go overboard when stocking fish. Too many fish in the pond creates an imbalance in water, so you'll want to make sure you’re smart about the number and size of fish that you place in the water garden.
Pond fish typically need 10 gallons of water for every inch of their length, but keep in mind they will grow larger over the years. So no matter how tempting it might be to add just a few more fish, be careful not to overstock! Some pond experts even go so far as to recommend only ½ inch of fish per 10 gallons of water as a maximum stocking density.
If you’re a fish fanatic, you may find yourself with a pond containing 2 or even 3 inches of fish per 10 gallons of water and the fish seem to be fine. However, the density and ecological strain of this loading can turn your pond into a fragile system. The pH tends to sag, the fish tend to grow more slowly, and disease can become a common occurrence.
It's very difficult to salvage sick fish in a pond that's overcrowded. Most likely, Mother Nature will sadly pick off your favorite fish to achieve her ideal stocking density based on the system the fish are in, and then the remainder may recover.
So before adding another fish to your koi collection, make sure you have ample space so that all your fish are ensured a happy, healthy home!