ice cubes are a no go, its a pretty big shock it its system and might do him more harm than good. most people i know who keep them have chillers on the tank, if i remember correctly the owner of the lfs i go to used to have one and he kept the temperature at 68f if i remember correctly, but yea no more ice cubes and id get the marine salt and look into a chiller
when puffers are in tanks that are too small for them, or they are not stimulated enough they "glass surf"
try putting intersting rocks and pieces of wood etc to make him have things to do. what size tank is he in? a 20 should be okay for a young one, but a 30 would be good for life.
I've never kept a fugu, maybe pufferpunk might post here as she is an expert on puffers. just take her recommended tank sizes with a pinch of salt though as they tend to be much too extravagant.
yeah that sounds about right there isnt much for it to do in my tank, looks like imma be heading back to the store to get hiding places for it to swim in and out of