Injected fins, that is, fins with dilated red vessels or reddish tinge to them can be a sign of several things.

• Stress
• Nitrate poisoning
• Ammonia or Nitrite accumulation
• Parasitism
• Bacterial sepsis (systemic infection)
  

So, for red or injected fins, you'd test your water quality, and if that's fine, you'd probably still be
well-advised to do a major water change and go ahead and salt the system.