I have three Schefflera arboricolas. Two normal, one variegated. All live together on top of a shelf in front of a window that receives a few hours of bright indirect light earlier in the day. All three are potted in the same peat and sedge moss/sphagnum/vermiculite/perlite mix. All three pots have drainage. Two are around two feet tall, while one of the normals is around one foot. They receive room temperature water (left out for 24-48 hours), and are watered when the soil is almost dry, just enough to keep them lightly damp. They've all been doing well, but suddenly the variegated one started getting brown spots on it's leaves and has begun dropping them. Most of the leaves it drops have the brown spots, but it's started dropping healthy green leaves as well. The other two plants are still completely fine. I recently moved them away from the variegated in case the problem can spread to them.
Here's how the leaves normally look:
Here's what's started happening:
I normally give the trees an occasional light mist with room temperature water because the house tends to get very dry. However, my central air system recently broke down and the house was incredibly hot and humid for a few days. The trees are on the upper floor, where the humidity was even higher. During this time, I did not mist them. I also put a small fan nearby to help keep the air moving (it wasn't pointed directly at any plants). The temperature and humidity has since gone back to normal, and I've refrained from any misting. I did just give it a water yesterday. The problem started right after the hot/humid spell, and has persisted over the last week and a half.
Any ideas on what might be going on, and what I can do to stop the problem?