The leaves will be wilted looking around the edges, and not as green (either yellow, or not their usual vibrant green). You need more potassium and nitrate.
If you need any (I know you're breeding) there's a post in the equipment classifieds.
If not, I'd maybe just trim the melting\ugly leaves for a while. Unless it has bad chlorosis, it will be remedied by dosing within days. Perhaps just pull the ferns in the meanwhile, fortunately they're a cheap and readily available plant.
What's happening is your plants aren't able to produce chlorophyll due to the lack of nutrients. I'm not sure if reducing the photo periods will help the situation, as the root issue is nutrients.