Same here... When I first posted the pictures of them sick, there was a resounding "flush!!" I ended up with bucket of mold and a half dead plant.
I am sure this works with Hydro, but IMHO, not with soil. If you think about it it makes sense. We put perlite in our soil to retain moister. Once it is full of bad shit (over nutes) it is there until it drys out or works it's way through the system. Pouring water over it does nothing as it is already saturated.
If I get a bad mix in the soil again, I will replant before I flush. It is easier, dry, and IMO, much less risk. Looking back, I should have just left them alone and only used water for a few waterings.