Yes, this is very likely the carbon dosing. It's a bacterial sheet a lot like cyano, but THIS one won't likely respond to a lights-out---different bacteria. Do this: 30% water change, wait a day, do a 20% water change, wait a day, do another 20% water change, then stop; likewise install a 1-micron filter sock and keep changing it daily (you will need more than 1, while you wash the other. Aerate like mad, and do you have a really, really good skimmer? You might also lay a paper towel or B&W newspaper on the surface where you have floating slime and pull it off now and gain. Do NOT run a carbon bag until this is fixed.
You could fix this faster by moving all specimens and fish and inverts to a qt tank for the duration and do several 100% water changes in the dt, days apart. This is why you don't carbon-dose except on an older tank with a good skimmer.
