1. Keep offering food on your normal schedule. Check your husbandry for any issues. Hides the right size, temperature gradient, humidity, etc.
2. Why aren't you happy with the 28 qt? Most people who switch to tubs never go back. Like I said above, husbandry issues could potentially be a cause. And besides, moving enclosures will stress your bp anyways, so you might as well do it now. But, I would make sure the tub can absolutely not work out before you decide to switch.