Water parameters and String Algae

The Algae is wild this year. I can pull it out by the handful everyday and
the pond is only 500 gallons. I finally put a few Water Hyacinths in on the
weekend, but they look a little off. So I tested the water tonight and
Nitrates and Nitrites are ZERO, PH is 8.4, KH is 180 and GH is 75. I haven't
checked the Phosphates, but they must be off the scale. I'm getting a lot of
bird droppings in the pond. I added some Potassium for now, but it looks
like the WH are going to need some Nitrates.

I'm a little reluctant to add Nitrates. I haven't been feeding the fish (9
GF) much, given all the Algae and bug life available. Do you think
increasing the fish feeding will help the plants? The Algae couldn't get any
worse anyway!