You could use a potassium permanginate dip but it is hard on BB so I wouldn't use it in the tank.
If I had to choose between amoxicillin or doxycycline I would try doxycycline it's similar to Tetracycline in it's function, it is effective against gram positive and negative bacteria so you will need to keep and eye on your water prameters. I have never used either one on fish so I can not vouch for how effective it will be or give you much help with it. It is well absorbed so it may be effective just be carefull with dosage. The only guid line I can give you is the doasge for tetracycline which is 250- 500 mg per 20 gallons of water (I would start with the lower dosage). Every 48 hours (24 hours for severe issues) with a 25% water change before each treatment. Tetracycline is ineffective in a ph above 7.5. Again I never used it so I can take no credit or responsability for your results with it.
If I had to choose between amoxicillin or doxycycline I would try doxycycline it's similar to Tetracycline in it's function, it is effective against gram positive and negative bacteria so you will need to keep and eye on your water prameters. I have never used either one on fish so I can not vouch for how effective it will be or give you much help with it. It is well absorbed so it may be effective just be carefull with dosage. The only guid line I can give you is the doasge for tetracycline which is 250- 500 mg per 20 gallons of water (I would start with the lower dosage). Every 48 hours (24 hours for severe issues) with a 25% water change before each treatment. Tetracycline is ineffective in a ph above 7.5. Again I never used it so I can take no credit or responsability for your results with it.