Hi, We also have the Koender's Windmill like Theo at our Pond which is about an acrea (going on 3rd year). There are a lot of these in the area here. Works great, aerates the pond, no fish kill and it does keep an opening in the pond during winter... would definitely recommend 20' height, too. My hubby and I put this one together in a weekend. Regardless what windmill(s) you decide on, it will make a difference and they are neat to watch (we see ours when we do our porch sitting and he can see the whole pond and windmill from his office).
