I have a Oncidium which has had tiny black spots on its leaves since I bought it and don't know why it happens or how to get rid of it. I just finished re-poting in fresh new medium since the old one was decomposing. Here is a photo.
I think that is it probable that those spots are due to misting/spraying the leafs. Oncidium leaves have a tendency to have spots when they are sprayed. Keep an eye on the spots just in case. If you see them get bigger or turn necrotic, it would be a good idea to treat the plant.
Also, just as a side note, I think you should probably pot it in a much smaller pot. Seeing the size of the plant I don't think it has a huge root mass. In a pot that big, the medium might not dry out quick enough and you might have root rot problems in the future. Normally you should select a pot size where the roots fit comfortably in it. To give you an idea, I have a young oncidium with 2 bulbs each about 2 inches tall (without the leaves) and it is in a 3 inch pot.
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Thanks for your reply. Rain is what usually waters my orchids since it rains a lot in south florida. So maybe I should protect it from the rain and water it myself making sure not to wet the leaves. Also when I took the picture it was before i re potted it, yes the pot was too big so I planted it in a 3" pot.