When you say large circulation fan, just how big do you mean? It almost looks like its damage from the leaves hitting each other under a high prolonged wind. If your blowing a fan directly on the plants, you shouldn't get too strong with it. They should look more like they are dancing and swaying as opposed to bending over in a hurricane.

However, it might pay you to look very carefully on the undersides of the leaves for tiny insects...as the pattern of decay sorta looks like leaf miners.