you mentioned the bulb melted to the acrylic cover which would imply the bulbs were covered at the time. i.e no cold water ever touched the bulb. that being said t5s do this from time to time. im an electrician so i fix t5s often. some t5s are wired in series some are not. what these means is if 1 bulb goes dead the other bulb will also not fire. like old christmas lights. first thing i would do is replace BOTH bulbs. its possible the other bulb that isnt obviously broken has failed as well. if they still dont light, you have a dead ballast. replacement ballasts can get quite pricey, depending on the model you need. for a cheap fixture it may be more cost effective to purchase a new one. good luck.