I'm with @Jhn on this one. I know the IonGen works, but my feeling is that anything that kills algae in the water is only adding more dead organic material to the water. You're treating the symptom instead of the getting to the root cause. Like taking Tylenol for a fever without figuring out why you have the fever in the first place. You need to strike the balance between the right amount of fish, plants, water, and organic matter in the pond - all things that are completely within your control. 2000 gallons is a good sized pond, but it's not huge. Hopefully you have more goldfish than koi, because as they grow, they will continue to contribute more and more waste to the system. More plants is probably the easiest thing to adjust, but you can also control the amount of feeding you do and reduce your fish load if necessary. Just see that algae as both a reminder and a solution - it's doing good work in your pond until you get the balance back!
