8 hours on seems just fine, sometimes if they are on for 12 or 14 hours it's just too much light. You could try product like Chemiclean, which will get rid of it, but if you don't figure out the root cause it will likely just come back. I fought it for a long time and ultimately it was reducing the amount I fed my fish that seemed to help the most! I now feed once a day, and I try to keep it small amounts. Fish all seem fat and happy, and I haven't had an outbreak in a long time.
Tank was also moved 4 months ago, could just be readjusting as a new tank would? Might just take some time, patience, and frequent siphoning, to get it under control.