Please help with yellowing Masdevallia 'Hampshire prolific'

[Ken]

Good morning all. I'd like to get some expert opinions on my Masdevallia 'Hampshire prolific' that is badly yellowing. The history: I've had it for roughly 1/2 year. I grew it for a couple of months on the windowsill until I finished my new orchidarium setup. Since then it has grown in the new orchidarium. In that environment, it gets 11 hours of light from a Quantum badboy that measures around 1100 fc at the plant. I water by misting every 2 h to the point where sphag gets nice and wet. I have fans to keep air flowing, and most sphag dries before the next watering, but not to a crispy point. I keep it so there is a little residual moisture at the bottom of the orchidarium to maintain high humidity. This Masdevallia has bloomed once very nicely, but it has continued to yellow more and more. My initial thought was that the roots were too wet and beginning to rot. It was potted in a small plastic pot with sphagnum and tree fern fiber, so I pulled it out to repot. As it turned out, the roots weren't in bad shape. I've remounted it on bark with light sphag, roughly 2 weeks ago. I've attached pics of the leaves and their yellowing below. My best guesses for what the problem is are: 1) not enough fertilizer; I haven't been religious about feeding this guy so that could be a problem, 2) too wet, I'm less inclined to think this is it, since the roots weren't rotted, 3) too cold; it gets down to 65 or 60 at night this time of year, up in 70s during the day, 4) too much light? is it possible that it's getting too much? I would think the tips would purple rather than the whole leave getting yellow, but not sure. I'd like to hear any ideas you have. As a reference, in one picture you can also see a Ceratostylis rubra that is showing slight yellowing too. I also have a happy Aerangis 'luteo-alba', and a slightly purple Masdevallia/Trisitella gemmata, and a relatively happy Dracula lotax, which may have just a twinge of yellow. I appreciate any help you can provide.
Thanks
Ken

[Ken]

It also occurred to me that my water is rain water collected in November with a little physan 20 to fight algae growth while the water is stored. Is it possible that the perpetual exposure to physan could be the problem.
Posted via Mobile Device

[Carolla]

I'm going to follow this one, I have a darling little Masdevalia which I got last summer. It promptly lost half its leaves which turned yellow and fell off. However, I repotted it and it has held up fine since then (though it hasn't grown more or bloomed again - no surprise it was in bloom when I got it). I really don't know a lot about it though. I have it next to my kitchen sink for bright light, cooler temps and better humidity. Also it needs watering more than my mature Phals.

[Katherine]

You say you are misting every 2 hours? I don't know anything about green house type set-ups, but it seems like a lot. I have a Masedevallia Falcata 'Red Sunset' and it is growing on my deck. Today it was a balmy 52 degrees. It is usually in the 40's. It is growing in spaghnum moss, and is very happy and healthy. The moss is very moist, vut with the humidity here I rarely water it. and only bring it into the house if I think the temps will go below freezing.