I'm going to make a couple of [potentially unpopular] comments. First of all, I don't think your pond of 1500 gals is going to be adequate for several koi and goldfish. That is a good size for just GF, however. Your questions about what fish eat in the wild have been addressed, but please let me warn you that koi tend to be/can be/have been known to be difficult keepers, requiring almost constant maintenance [and yes, there are exceptions]. What bothers me about your comments is that it sounds like there might be frequent and long trips away from home. With all that can go wrong with a pond, I would rather leave my fish UNDER fed while I was away. In the event that there was a [free-feed] malfunction with the feeder, or if there was a fishy illness, or other environmental issue......there are times when you want to cut back on feeding, but if you aren't there to monitor the pond conditions, your fish could be overfed [with a very bad outcome]. Problems like this would be even MORE of an issue with koi. Now, that being said......there are TONS of people who have auto-feeders, and they probably never have any issues. Just IMHO, and not trying to stir anything up......just wanted to point out something you may not have considered.