Before introducing new fish into your tank, they should be quarantined. This is to prevent the fish bringing in bacteria, parasites and disease from outside. You cannot skip this process; otherwise it will give you endless of disease problems.
You will quarantine your fish in a special tank using the steps below:
1. Give the new fish a Potassium Permanganate (PP) bath
PP Dosage: Pink to dark purple in color. One day is enough. If you feel like to continue then change the water and repeat the treatment.
Potassium Permanganate Medication
3. Apply acriflavine solution with salt or Apply antibiotic plus salt for a week
4. Keep the fish in this tank for two, three weeks
5. If you think they are okay then you can mix your new and old fish together.
6. To confirm your okay:
Take one fish from main tank. Put her into Quarantine tank for a few days. If everything is okay then transfer the new fish to the main tank. We are not sure your local fishes have disease or not but one thing we are sure every fish farm they are certain bacteria or parasites incubating in the fish. They can tolerate because they are already immune to it or they have antibody to it.
So, when two different farms fish mix together without quarantine, what thing will happen? 9 of 10 times the fish will get disease.