Thanks for updating us on your progress in treating the fin rot, sir! It’s good to hear that the seahorses responded to the hyposalinity well and that the black area has decreased notably since you reduced the salinity.
It’s okay if you want to observe the seahorses closely for the time being and see if their tattered dorsal fins begin to regenerate without further treatment, just don’t delay too long if you do not see clear signs that the fins are repairing themselves soon. You need to be aware that if the fin rot is allowed to progress to the point where the fin has eroded all the way to the body, thereby allowing the infection to invade the underlying musculature, the prognosis becomes very poor and it is unlikely that the seahorses can be saved at that point. In other words, if you delay medicating the seahorses too long, there comes a point when it is too late for any treatment to be effective. In my opinion, the sooner antibiotic treatment is begun, the more likely a positive outcome becomes when dealing with fin rot.
In addition, there is a good disease book on seahorses that you would find to be helpful if you don’t already have a copy, sir.. Dr. Martin Belli, Marc Lamont, Keith Gentry, and Clare Driscoll have done a terrific job putting together "Working Notes: A Guide to the Diseases of Seahorses." Hobbyists will find the detailed information it contains on seahorse anatomy, the latest disease diagnosis and treatment protocols, and quarantine procedures to be extremely useful and helpful. It has some excellent dissection and necropsy photos as well as a number of photos of seahorses with various health problems. This is one book every seahorse keeper should have in his or her fish-room medicine cabinet, and I highly recommend it! In time of need, it can be a real life saver for your seahorses. It’s available online at the following web site:
Best of luck healing your seahorses’ tattered fins, Dodge.