If those are your real temps and humidity it isn't that. I've had plants deal with much worse conditions. I would definitely guess it's that soil and I wouldnt' flush it. Just don't add any more nutes to it and just use plain phed water. It's not a deficiency I've ever seen.
Use plain water and check the ph of your runoff religiously and in a couple of weeks you'll be back here ecstatic they look so much better.