Three of your fishes died the other ones look like they were sprinkled with salt and also their fins rotted away will health restore back to normal is it infecting?

It's possible that your fish are suffering from a bacterial or fungal infection. Some of the symptoms you mentioned, such as body discoloration, fin rot, and death, are common signs of these types of infections. It is important to identify the exact cause of the infection so that you can take appropriate steps to treat it. Below are some tips for diagnosing and treating fish infections:

Examine the fish closely: Look for any signs of physical damage, such as cuts or abrasions, which may be entry points for infection. Also check for any changes in behavior, such as loss of appetite, lethargy, or erratic swimming.

Test the water quality: Poor water quality can stress fish and make them more susceptible to infection. Check the water parameters, including temperature, pH, ammonia, nitrite, and nitrate levels, and make sure they are within the optimal range for your fish species.

Identify the pathogen: If possible, try to identify the specific pathogen causing the infection. This can be done by taking a sample of the affected fish to a veterinarian or fish health expert.

Treat the infection: Once the pathogen has been identified, you can start treating the infection. There are a variety of medications available to treat bacterial and fungal infections in fish, some of which include erythromycin, kanamycin, and malachite green. Make sure to follow the dosing instructions carefully.

Improve water quality: In addition to treating the infection, it is important to improve the water quality to reduce stress on the fish and prevent further infections. Perform regular water changes, and use a water conditioner to remove harmful chemicals.

Quarantine infected fish: If possible, quarantine any infected fish to prevent the infection from spreading to other healthy fish.

It is important to address the problem as soon as possible, as fish infections can quickly spread and cause significant damage. If you are unsure about how to diagnose or treat the infection, consult with a veterinarian or fish health expert.