How big is your tank ? Is it the whole length of the tank? You dont want a fixture the whole length of the tank ---- he needs to be able to get out of the UVB rays if he wants to that is why I suggested the 24" fixture --- see if you can find a 20" fixture from your local petstore --- even if its a Thrive brand or Zilla-- you can ditch the bulb it comes w/ and use a Reptisun 10.0 bulb and it would be a T 8 and it would need to go inside the tank approx 8-10 inches from your basking decor --- work on getting that replaced and I would take him to the vet ---- the vet you have is experienced w/ reptiles?????????? Here is a website for finding a vet
http://www.arav.org try that and see what comes up
Its great your getting him out for sun that has helped I am sure but w/ you saying that something else could be going on as well -- but you still need a better UVB --- that coil is NO good
Karrie