You can flush your plant and have good results! It is not really a last ditch effort! I flush mine every two weeks or so! Just pour clean PHed water through the soil like 10 times your container! If you have a one gallon pot then pour ten gallons through it! Then on the last pour use 1/4 or 1/2 strength nutes! Then let it sit a few days before you water it again! Also get the majority of those sick leaves off! They will keep it from getting better! I promise you will have good results if you do it right! Other wise they will die!