Since amoxicillin paste seems reasonably active in SCTLD, it is likely that at least part of the disease is due to a relatively antibiotic susceptible bacteria. That does not mean that the disease is not multifactorial. It could be that water temperature, a viral infection, or other insult, allows for the bacterial infection responsive to antibiotic treatment.
It is frustrating that the etiology and effective treatment of SCTLD is not better defined after 7 years. Unfortunately, this seems like a very complex disease.