aquatic plants in the system

I currently have a 150 gal. tank with about 4 lbs. of koi, water hyacinth and duckweed. Plants are harvested for farm income and fodder, respectively. This is a prototype system that I hope can be scaled up when my high tunnel goes up and I gain more knowledge and experience. 2-3 times a week, about 10% of the water is used to irrigate nursery plants and replaced with a cool, oxygenating blast of tap water.
The tank has been up for 3 months. Is this water usage sustainable or am I risking an imbalance in the ammonia/nitrate ratio?

Do the aquatic plants significantly affect the fertilizer value of the water? Could the water be used in a recirculating system with good results?

Thank you!