Your water params look ok.
What has happened in your tank since your last posting in early January, about a month & a half ago ?
Did you keep up the large, frequent wcs, and the tank cleaning routine ?
How are your discus doing now ?
Fill us in.
The oily film on the surface of your water indicates a high level of dissolved organis in your water. In other words your tank is dirty. Do the reccomended w/c running some activated carbon in your filters will also help. Dont forget the wipe down and gravel vac.