I have started fertilizing them, first just compost tea, and recently with hydrolyzed fish fertilizer.. I think they have improved a bit since I started with the fish fertilizer. Hard to tell for sure, definitely haven't gotten any worse. So maybe they just need more nutrients.
I water them with well water.. The PH is 7.3
It wasn't a sudden change or anything. They've pretty much been this way since I brought them outside in the spring. Before that, they were in my aquarium set up with very high humidity, and a constant 85F, under LED lights. They seemed OK in there at the time, but they outgrew that.. They're out in the world now =) I might try putting one of the smaller ones back in just to see what happens.