Although it might work, it may cause problems on down the road. I would think that it would be absorbed by the rock and sandbed if you have one and slowly release back causing abnormal fish behavior. Even with large water changes youd only be diluting the oil and I suspect it would take some time to be completely gone. Ive had tremedous luck controling Ich by O2 deprivation, raising the temerature will hinder its ability to thrive, feeding well along with good water perameters will usualy help, maybe even the temporary use of a good UV sterilizer.