They may not need a flush; check your soil runoff pH first! And check the COLOR of the runoff... it should be fairly clear, if a bit dirt-y. If that makes sense. If it's yellowish, keep flushing, lol. And if the pots have drip trays built in, take them off before flushing, as they will block the drainage!
Oh 12/12... only if you want to flower right away. You might want to hold off and keep them on 24/0 until you are certain that they are perfectly healthy. It is harder to fix shit in flower.
You are making me blush! I gotta run, back Monday.