I have several catts and minicatts with leaves that turn black and fall off. What causes this? I don't see evidence of insects.
You may have a bacterial rot. Keep your orchids cleaner & don't overwater. What is your temperature range? How many hours do you have the lights on? You could also have a physiological problem due to temperature or daylength.
<<They are just under fluorescents and not many of those.>>
Maybe you need more. Cattleyas thrive under four fluorescent tubes.
<<I also have some catts with leaves that are almost rose-coloured. They used to be green. I know this can be a sign of too much light, but they are just under fluorescents and not many of those.>>
On the contrary, this is a sign of health, and that the plants are getting enough light. It is the plant equivalent of a suntan. If your Cattleyas were getting too much light, they would be bleached yellowish, which is not likely under fluorescent lights.
Iris
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