First indoor LED & auto grow bp1500

Day 28 newer growth tips are coming out yellow so first time watered heavy, my first run off was 2150 ppm 😯 no nutes used yet so I'm guessing it must be from organic breakdown considering it tested at 600ppm b4 I potted up, got it down to 1200 after 20L of ph water per pot with about 50%run off , ph was 6.5 going in and run off is at 5.5 still, i think this could be due to me using citric acid powder to lower my tap water ph and it has somehow built up, next water I'm gonna flush with straight tap water, ph of tap water is 7.5 cheers