I have only flushed one plant out of the hundreds I've grown and it didn't change shit so not sure that you should flush at all. Maybe just water it good with nothing but a full dose of CalMag and pH it to adjust the pH you think you have in the pot.
I knew mine had gone high so I watered it with pH5 to bring it down then a day later added enough RO water to force some more runoff and it tested at pH 6.3 and 710ppm. Plant still don't look great but it seems that damage to the leaves has halted. Few days ago I gave her a good feed of 1g/L Mega Crop, 1ml/L CalMag, 3.5g Big Bud and 5g of the Carbo. 7L is usually the most she'll take but was almost 8 before water seeped out the bottom but no real runoff. pH was 6.1 and I forgot to check ppm. Yesterday she got almost 8 again but just 3.5g Big Bud, 1ml/L CalMag and 1tsp carbo. Today is day 30 of 12/12. and the buds are a lot smaller than they should be so hoping she bulks up good now that things seem to be a lot better.