Have you tried krill, mysis, bloodworms, or chopped earthworms? In my experience with Tigs so far (I've brought in 16 so far) some can be picky eaters and will only eat certain foods until they become comfortable enough. I've had some that would go nuts at mysis, while others in the same tank wouldn't touch it, and vice-versa. Earthworms seem to be a favourite of almost all of the tigs I've had go through my tanks so far.