two catts, two problems

[fishmommy]

I usually have great luck with catts, but I have two giving me the business lately and am wondering what I am doing wrong.

Catt 1. It's a monofoliate and has bloomed reliably for years. This year I had two sheaths (sequential, not simultanious) and two buds each. Within a few days of the buds actually opening, they'd fall off. The stumps of the spikes are blackened.

Catt 2. Bifoliate. Sheaths plenty, but the sheaths turn brown and no spikes develop.

Light is about 3000Fc HPS. They are potted in plastic with medium bark. I water very lightly but every day. Some aerial roots are present on the monofoliate but no the bifolate. I recently repotted both and the roots looked fine.

Advice?