Just thinking off the top of my head. You have a water source but it's full of nutrients, and if you divert it you could have problems filling you pond with the increasing droughts we seem to be experiencing long term. Maybe this could be attacked in several ways. Perhaps the water drainage into your pond could be planted with good filtering plants. I always used KOI and Israeli carp for FA control but why not also add tilapia for a triple mix and Golden Shiners for your minnow base as some believe they may have some effect on FA. For plants corkscrew ell grass only grows about 6 inches tall but to get it wide spread you need to keep replanting the off springs all over the more shallow parts of your pond. Other types of eel grass that grow taller might be planted in the deeper parts of you pond. Still I don't see how other types of water plants won't get into a nutrient pond, and that might call for some grass carp. My grass carp for the most part seem to leave my ell grass alone. You could always use copper sulfate for FA control like some do in my area.