Very hard to say much without an exam and an audiogram, or knowing much about the dive profiles. Tinnitus is poorly understood in general, but if it suddenly started while diving, that suggests some connection. Is there any hearing loss? It sounds like there might be, so an audiogram can distinguish between a conductive hearing loss and a sensorineural hearing loss, which have different implications. Here is some
background reading on these issues.
Inner ear DCS is certainly treatable, but you may be beyond the time frame for that. Barotrauma of the middle ear can result in an inner ear injury, especially in cases of a perilymph fistula. In such cases, surgical exploration can help, but this is a complex decision tree. Middle ear effusion from barotrauma alone would rarely cause tinnitus. If there is a sensorineural hearing loss that is not related to diving, then steroids are occasionally helpful (although not a lot of support in the literature when you look at meta-analyses).
I think that it might be a good idea to
call DAN and describe the details.
Good luck!