I think it's an ammonia issue. a 2.5 needs one 50% and one 100%a week. ( a 100 includes complete removal of the fish and thorough rinsing and drying with HOT water. no chemicals though! make sure there's no chlorine water left from washing. )
this is probably what's wrong with the behavior...
as for the coloring, it's not unusual for fish to get silver there... so I wouldn't worry about that alone ^-^;
20% a week for a 2.5 is not enough though ^-^;
the 100 is essential for a 2.5 because ammonia builds up on the sides and decor. in a cycled tank the good bacteria take care of that, but in a 2.5 it won't.
when you make the 100 make sure to clean the gravel really well and get all the debris out.
I hope he'll be alright... ^-^ <3
remember to acclimate him to his water before adding him back in.