Had them about a year. They are under 2 led radions in a 120 gal. Prob guilty of not directly feeding them ~ best time at night when sweepers are out ?
Are you certain nothing stung them?If it looks like Brown slime around the area you may want to dip.I would frag off the effected portion if it continues to get worse.
Definitely frag off the dead parts and keep it in an area of moderate flow. I notice candycanes tend to die like this if they are not receiving adequate flow through the heads and develop dead areas.