Hi
I have a PureAire model and although you buy specific oils for it, I experimented months ago with my own oils. It works just the same but at first the water goes a little cloudy, although the water eventually clouds as it filters the air anyway.
Essential oil tends to float on the top but it still clears and ionises the air, emitting a slightly stronger aroma compared to the 'proper ioniser oils'. I tried mixing my own oils with carriers first but found just adding oil was fine.