I....think your humidity gauge might not be working right. A tank filled with damp sphagnum with a lid(the lights comprise the lid, right?) should have a higher humidity, shouldn't it?
Anyway, if you changed and put the plants in pots sitting in the tank, you could use the tray method(having them sit in a thin layer of water maybe 1 cm deep) during the growing season and that would suffice.
What do the rest of you think?