Here's the rule of thumb when it comes to feeding your koi or other pond fish: Don't give more than your fish will eat in a few minutes.
Koi and goldfish are pretty good at telling you when they're full and will generally ignore excess food once they've had their fill. The good news is this means fish rarely get fat. The bad news is any extra bites will sink to the bottom of the pond and decay, affecting oxygen levels and overall water quality.
Feed your fish somewhere far enough away from the skimmer that they have enough time to eat before the filtration sucks it away, and watch to make sure they're eating just about everything you throw in the pond. Most people like to hold these feedings anywhere from one to three times per day.
Feel free to supplement meals with snacks like Koi Krunchies, grapefruit, watermelon or Cheerios. Your fish will love them, take in some extra nutrients and maybe even learn to take treats out of your hand. Make sure, though, that you don't overdo it to the point that you have excess food mucking up your pond.
Do you need to hire a koi-sitter if you go on vacation? Probably not. Pond fish can fend for themselves for quite some time just by snacking on mosquitos, insect larva, baby fish or your pond plants.
The one time that you should NOT feed your fish is when water temperatures consistently drop below 55 degrees for the season. Your fish might still act hungry, but their metabolisms have slowed down considerably. That means all those treats they wolf down will just sit in their stomachs. Store your fish food in a cool, dry place until spring, when you can restart daily feedings.