You will get the more experienced people on soon, but Cutrin Plus granules worked well for me. It also comes in a liquid form, but only do about one-third of the pond a t a time to control oxygen depletion as the algae dies. If done all at once it might kill your fish. I think chelated copper sulfate is the item that does the work. If I remember correctly you can buy that also at a feed store or chem distributor. Hopefully you will get more answers. The Koi would probably work fine since you don't care about fishing. I put carp in my tanks (or ponds) even tho they supposedly don't go for algae as their first course. Good luck.