With the koi in the pond you might not be able to clear the water. If they keep distrubing the bottom sediment the problem will never go away, even with the alum.
Go ahead and add it, but if it clears up then gets cloudy again, I'd do a test in a 5 gal bucket with the alum. If it clears with the same alum ratio that you used in the pond, then I'd suspect the koi.
