Help!!! Theres something wrong with oncidiums

Don't water based on a calendar. You are probably providing too much, and rotting roots. Instead, water when the medium is almost dry. There are several ways to determine when to water, but the easiest if you are new to this is what I call the "Pencil Trick:" Take a sharpened wood pencil, and stick it about half-way down the pot. Let it set for a few minutes, then pull it out. If the end is damp, you probably don't need to water. If it comes out dry, you do.