I own a pond in Lancaster Pennsylvania, which experiences huge algae growth in summer. Fertilizer runoff is a known problem and cannot be prevented. The current (3/15/18) PH is 9, Phosphate is .50 to 1.00. Ammonia is .25. Nitrate is zero. How should I treat?

I have a new pond 3/4 acre 10' to 3' deep soil sample ph 8.2 alkalinity 180 pond is fed by 2 springs and runoff from heavy wooded mountian hardwoods water ph runs 8.0 to 12 in late afternoon had problem with cotton diease on newly stocked bluegill what can i do to stablize my ph