Thanks KoiRun. Not an old pro, very much an amateur. First make sure you've got a mix of male and female. Sounds stupid I know, but I once misidentified a chubby male as a female, and it did not work ... until I pulled him out of the spawning tub and put him in the girls' pond
. Sometimes they don't spawn when I want them to. Having something to spawn on is important, such as spawning brushes, spawning ropes. Of course if you have plants, that will do, though most koi folks don't. Some use artificial Christmas garlands. Water temperature is a key. Some say around 72 F (22 C) or so is best, but I've seen them spawn anywhere from the lower 60's (17 C) to the upper 70's (25 C), and occasionally even outside of that range. As far north as you are, I wonder if it would take until late June or something, unless you heated the water. Changes sometimes seem to set them off, like a significant water change, just moving them to a new pond or tub, or a rainstorm or cool front blowing in. Some say they like a full moon, but I've seen them spawn at all stages of the lunar cycle. I don't know of any one thing or combination that always works. Usually doing the above will work, but you may have to give it time. Sometimes I've left mine in the spawning pond for many days before they spawned. Best of luck!