Hello everyone. I have recently started growing salad and leafy vegetables recently,but I have encountered a few problems and would require some advice. I have 5 200liter-barrels of water in which I keep about 15-20 tilapia fish. They each supply nutrients for 25 PVC pipes,each containing 20 netpots. My first grow was with pakchoi,and the results were promising,but the second,again with pakchoi,and third,with lettuce,were of very poor quality.What could be the issue? Do I have to change the water more frequently?(I change the water about once every month,and each time the water is a bit dirty) Please advise.