Grow Mediums Flush?

[Bongos]

This is my first go at RDWC. Everything has been going well. My question is about flush. She has been humming along at pretty low strength, Maxed out at 550 ppm with a touch of tip burn. She really liked being around 400. Looking to harvest this weekend possibly. Ive been adding nothing but RO water, ppm at 230 now, checking trichs daily. I guess what I’m getting at, is do I really need to empty out res and refill with new water at this point?
thanks

 

[Trichome farmer]

This is my first go at RDWC. Everything has been going well. My question is about flush. She has been humming along at pretty low strength, Maxed out at 550 ppm with a touch of tip burn. She really liked being around 400. Looking to harvest this weekend possibly. Ive been adding nothing but RO water, ppm at 230 now, checking trichs daily. I guess what I’m getting at, is do I really need to empty out res and refill with new water at this point?
thanks

i would go by how much the plants have faded if there still dark green then you need to go a bit longer if they are yellowing out then your all good thats the best answer i can give without a picture