Overcrowding and overfeeding kill more fish than all the parasites combined.

The majority of hobbyists, if they were to make a feeding mistake, would overfeed. This is because the feeding process is arguably the best time you have with your fish. At feeding time, Koi come up to eat so you can see them, and anyone with a maternal instinct will thrill to watch their favorite fish engulf food with such Koi-ish zeal. Overfeeding is engaged anytime the fish are eating more than they need. So, for a fish farmer with a mud pond full of small fish he's trying to grow, he would feed about five to seven times per day. That would not be overfeeding. But in a typical ornamental pond with a reasonable collection of fish, that feeding rate would be excessive and the wastes therefrom would strain the limits of what can be biological reduced. Means: You water quality will decline. 

Fish that are overfed in typical ornamental pond facilities will eventually develop ponderous bellies and begin to look a little bit like tadpoles, with the big body and the wispy tail. That is not a terminal event for the fish but the impact on the liver and other internal organs can and will be severe. Farmed fish that have much more room in lakes or large ponds can be fed considerably and they will not develop as much obesity as reguar backyard pond fish. 

Fish should be fed no more than three times per day. In cooler water they should only be fed once per day, if that. In much warmer water, three times per day is not 'crazy' however, you have to be wary of bacterial blooms (cloudy water and low oxygen levels) if you feed heavy and there's a lot of waste. 

Fish should be fed for about five minutes per feeding. If they don't come up and eat voraciously, they are telling you that they are too cold, or too warm, feed light. If they come up and "hit hard" you can sprinkle food on the water for five minutes as long as there are fish there to carry it off. Pretend it's a game, NEVER LET IT FLOAT. So, feed the fish as they approach and let them carry it all away, leaving none to float into the skimmer or filter.