I am working on a .75 acre pond that was a liquid manure (dairy) storage pit at one time. All of the liquid manure and solids were removed about 15 years ago. There is no runoff water that enters this pond, only what hits the water surface from rain. I have to drain a couple feet of water off of it a year to keep it from breaching the banks (no spillway). The banks are steep because it was built for storage capacity not aquatic structure. There were no fish or minnows present until I stocked it with 25 lbs of fathead minnows, 200 2-3" bluegill and 50 5-8" bluegill. I do not feed the fish. I used a cast net and minnow trap like advised and only caught tadpoles before I stocked. My goal is to add a few bass next spring or fall. The only plant life are a few plants on the steep banks (less than 2' of plant life due to deep water) and they are mostly common weeds like curly dock, smartweed, velvetleaf. I have never seen any stringy algae. Occasionally there will be a duckweed and watermeal bloom. It may cover half of the pond but never very dense or out of control. Clarity has ranged from 18-30" this spring.
My levels are:
pH 7.5-8.0
Phosphate 8-10 ppm
Nitrate 0-.1 ppm
Ammonia 4-5 ppm

What do I need to do to make this pond better from a fertility standpoint? I farm and have fertilizer and lime readily available. If I left out any details just ask and I will answer to the best of my ability! Thanks