Sick cattleya
 

A few of my cattleyas has some Black spots. What could it be? The spots have been developing over quilte some time (months). The plants are in side my home, and stands under lights.

This is bacteria/fungus. From the photo it seems you have a lot of plants close together. Chances are one developed bacteria and then the splashing from watering that orchid allowed the bacteria to spread to other orchids in the group.
If it is really bad, then a systemic insecticide & fungicide once a week for 3 weeks then once a month thereafter for maintenance. If its not too bad then spraying them once a month will work fine.
Good luck.

I agree, it looks fungal or bacterial. Try to water in the morning and have good air movement so plants are dry by dark. I agree, a fungicide should be used to stop the spread.

It looks like fungus. I would recommend using a systemic fungicide on regular basis for a few months. I use one every three weeks. Also get the plants into an area where they get good light and plenty of air movement. Don't crowd them together.

Thank you much for your answers. I Will get some fungicide.

Can anyone recommend a good systematic fungicide that they have had good results with? Thanks

Biolife, or physan.

While looking, isopropyl alcohol will help keep it from spreading. This is what I use on indoor plants. The others are better as they do not need to be applied twice daily. :)

I´m not sure i know isopropyl alcohol.
Do you think i should cut of the damaged leaves, so the fungi dont spread?

If sections of the leaf are looking soggy and mushy to the touch I usually cut down to the section of the leaf that looks healthy and feels firm. Then I just dab on some cinnamon to the "open wound" to prevent any infection.