Could be Lymphocystis; I have sometimes seen it manifest in this way. The other possibility is a bacterial infection of some sort. Either way, I would start off by soaking his fish food in vitamins (Selcon, Zoecon, Vita-chem) for the time being. If it gets worse, I would either soak Kanaplex (an antibiotic) in his fish food using Seachem Focus as a binder or ideally, treat with Kanaplex by dosing it directly into a QT.