Happy Birthday ICMag! Been 20 years since Gypsy Nirvana created the forum! We are celebrating with a 4/20 Giveaway and by launching a new Patreon tier called "420club".
You can read more here.
Important notice: ICMag's T.O.U. has been updated. Please review it here.
For your convenience, it is also available in the main forum menu, under 'Quick Links"!
I would water with plain water until you see the burn go away. Also make sure and keep your pH in proper range and you should be good to go in a week or two.
please note, the burn will never actually go away (leaves do not repair themselves in this manner) the post above means when you see that the new growth has no burns, that the burn has gone away
You cannot flush nutrients out of the plant, so this is about starving it of any new nutrition.
25 gallons of overfed soil will need ~75 gallons of water at each watering for at least 3 waterings. After the 3rd watering you can reduce the level down to about 25 gallons of water at each watering until the plants finish. Don't water too frequently, allow enough time for the soil to reach a healthy point for another flush before repeating. Depending on the size of your plant it could be 4-5 days between each one, so this could take 2 weeks+