Isn't the filter deposited right on the CCD chamber window? If that is the case it can't be moved, only replaced. Checking the QHY8 webpage, many of the pics there have a halo too. Perhaps they (QHY?) can replace the window with one with a better coating? Or you could add a UV+IR blocking filter in front, if the offending radiation is NIR. For example the SBIG ST-4000XMC has a custom coated CCD chamber window, see here:
http://www.sbig.com/sbwhtmls/special..._st4000xcm.htm
and here:
http://www.sbig.com/sbwgifs/baader_uvir_filter2.gif
EB