I also thought of a way to simplify adding the "fertilizer". Thanks to our local Pepsi distribution center, I have access to 13 gal. & 55 gal plastic barrels. My idea is to submerge a covered container in the pond so that the top is a few inches below the surface. Leave the "plug" out, or cut a 1" to 2" hole if using a 5 gallon bucket with lid on fast. Run a hose out and to the bottom of your container. Liquid fertilizer can then be poured down the hose and will come out at the bottom of your container. This will force liquid out the top that has been diluted, leaving full strength solution always closest to the bottom of your container.
This should allow you to regularly add "fertilizer" without worrying about concentration, and without having to go out on your pond.
If you plan on collecting and adding large amounts, set it up so that the "fertilizer" drains slowly into the hose from your source on shore. That way it will also be slowly mixing in with pond water at the top of your container.