Flush problem

Hi first time in hydro grow has gone great

I was overdoing the PPM in my RDWC up to 1200 until I got nutrient lockout I reduced the PPM for a bit then started flush

I have been flushing with pure RO for 5 days now the buds are ready for harvest but the flush/leach hasnt worked the leaves are still a healthy dark green top to bottom I guess from me overdoing it for so long

I found some canna flush in the cupboard and added that now running my drippers constantly with the flush

My questions are

Should I have used the flush before the past 5 days of RO water?

How long should I let the flush drip through my hydroton? Few hours? Days?

After this flush sould I then do a tank change back to pure RO water and give it another week for yellowing or will the buds be okay even though the plant doesn't have any yellowing?

I know a lot of people say flushing a myth but I'm saying if it's not a myth will it be okay?

Flush yer toilet not yer weed

Generally you lower the feed for the last 2 weeks then maybe 1 week or 5 days plain water.

But if you blasted them with food till harvest it is going to take some time to get a fade.