Hmmmmmm...
What frozen shellfoods are you trying? Coz normally if you soak their food in garlic they at least give it a try...
You could also also try defrosted shrimp as well by either tying the end of it loosely with some thread or get some long tweezers type thing to try and dangle the food infront of his face to see if you can intice him to eat...
Im also guessing maybe the lack of decor could also be causing issues since they do like to feel safe when young and lack of decor + lights could be stressing him out...
Finally lets also not forget that ips meds can do a slight number on puffers, so that could also be a contributing factor...
Hope that helps
What frozen shellfoods are you trying? Coz normally if you soak their food in garlic they at least give it a try...
You could also also try defrosted shrimp as well by either tying the end of it loosely with some thread or get some long tweezers type thing to try and dangle the food infront of his face to see if you can intice him to eat...
Im also guessing maybe the lack of decor could also be causing issues since they do like to feel safe when young and lack of decor + lights could be stressing him out...
Finally lets also not forget that ips meds can do a slight number on puffers, so that could also be a contributing factor...
Hope that helps