Frank, I have been trying to figure out fertilization for my middle Ga pond also. The DNR recommendation might be OK but I think you can spend your money better. The 20-20-5 sounds more like a lawn fertilizer. You toss this in the pond it is going to the bottom and much of it will not be used.
I am going to use a 10-52-4 water soluble fertilizer made for ponds. Will get mine from Greg Grimes.
Where's your pond, mines in Putnam Co. near Lake Sinclair.