He could very well just be at that age where is "baby metabolism" is changing to "adult metabolism" ... I would cut back the feedings to once every 2 weeks and see if that helps.

Make sure he's warm and is getting 12-14 hours of light a day ... it's that time of year and he's at that age where he might be thinking more about the ladies than food.

I wouldn't think that F/T has anything to do with it.

-adam