what fert

hi all. Im growing misty and papaya, 3 weeks into flower and the leaves are a bit too yellow for my liking. I think its a N defic and maybe a case of slight overwatering. I am feeding miricle grow 15 30 15 started on 1/4 strength 2 weeks ago. Q is, should i flush before i feed? what should i feed with? a high N or 20 2020. oh yeah im growing in miricle grow soil with perlite and virmiculite under a 400w hps.
thanx

In flower cycle use less Nitrogen. The older bottom leafs will yellow and even fall off over time, this is normal.

Good Growing!