Cattleya sheath rotting from tip

Cattleya gaskelliana cross had a new growth about 3" long which started to rot from the tip.
I caught it when it was about an inch down the growth and cut it off at the base.
The rest of the plant looks great, light green leaves with a touch of red "sun tan".
All I can think is it didn't like the fan that was quite close to it all day and night (thought air movement was supposed to prevent these things).
Never gets below 50 degrees in the greenhouse.
Could have kicked myself after I made the cut I saw a tiny root starting just above where I made the cut.

Tell us about your water. You think it might be a calcium deficiency?

I use rainwater exclusively and MSU formula fertilizer which I stopped in October and will resume this month.
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No guarantee of course, but that might have been the issue.

Calcium is an essential element to actively growing tissue. However, unlike most other nutrient elements, once it is absorbed by the plant, it is pretty much "locked" in place, so cannot be shifted from old tissue to new as needed. By using rainwater and stopping your application of a calcium-bearing fertilizer, you completely cut off the supply, right when it needed it most.

That leads me to ask, why did you stop feeding?

I plan to change my feeding routine to a constant year round one.
I've seen much advice to stop in the winter but seeing that many of my plants are putting on growth over the winter in the greenhouse I can see this was not a wise move.
I've only been growing orchids about two years now but have been learning quite a bit, thanks for your input here.