Jewel orchid leaves going bad

[Nish07]

Hi,

I have several jewel orchids set up in a sealed tub (for humidity) planted in sphagnum with drainage. I think the conditions are fine and the ammount of light they're getting isn't too great. However, the leaves are starting to look burnt and chewed around the edges. Even new leaves are growing with spots underneath them where they look like a pest is eating at them. I'm fairly sure it isn't slugs as I got rid of that issue some time ago and the way the leaves are chewed (or burned) isn't as it was with the slugs.

Do any of you know what it might be that's causing this and what to use? I do not want to use a heavy insecticide as I plan on transplanting these into vivariums with frogs at some point.

Thanks,

-Nish