systemic fungicide use on lepanthes?

[mremensnyder]

Hello, I have 20 Lepanthes species growing in a cool growing terrarium. Recently I have noticed a few have started to get some leaf spots/black leaves. Can I use a very small(like 1/4) dose of systemic fungicide on these to keep fungal infections at bay? I know they are sensitive to chemicals. If not, what should be used? thank you all.
-Michael