@Johnny d. If I remember correctly you have a rather small pond - under 300 gallons, correct? If that's the case I would suggest that you are already fully stocked with three goldfish and a small koi... which will very quickly turn into multiple goldfish and a not at all small koi. In fact, I would recommend you find a new home for your koi before it overgrows your pond and throws you into another kill-off situation.
These small ponds are best suited for a few colorful goldfish. And yes, 300 gallons could hold more goldfish than 3, but like I said - give nature time and you will soon have many more than that.
Just an opinion... again, the only goal is to lead you to happy pond ownership without the problems you have experienced recently.