I'm thinking about one of these TaNg to combat your reoccurring bud rot issue http://www.growell.co.uk/cleanlight-air-purifier.html my personal opinion is you're using a dehumidifier to get the humidity down to suit your budding plants, whilst your babies are in need of humidity. Maybe the mature ones are going into mothering instincts and sweating out to cater for their humidity demands. The laws of nature is it all works in harmony for each other. Even ugly death is compost food for pretty roses.
Plants grown under LED like the RH low (between 35-45%) in veg too,the RH hasn't bern over 45% for the entire grow so there is nothing more I can do RH wise but your right about the air purifier I was looking at them a few months ago but it slipped my mind to get one. Didn't loose much so I'm not fussed.