I’m sorry to hear about your seahorses. It’s great to know that they are still active and eating well. While I can offer some general suggestions, I’m not a veterinarian. It’s important to consult a qualified aquatic veterinarian for accurate diagnosis and treatment recommendations.
Flesh erosion in seahorses can have various causes, including bacterial infections. Chloramphenicol (Chloromycetin) is an antibiotic that’s sometimes used in the treatment of bacterial infections in fish