scaleless fishes couldn't use salt, especially catfishes
This is not true. There are many catfishes that can tolerate 3ppt-5ppt salt, and many scaleless fish that can tolerate it. The key is splitting up the dosage of salt used across 3 days or more.
1 gram of salt per 1 litre of water volume of day one. (1ppt)
Add additional 1 gram of salt per 1 litre of water volume of day two, so tank has total 2 gram of salt per litre (2ppt)
Add additional 1 gram of salt per 1 litre of water volume of day three, so tank has total 3 gram of salt per litre (3ppt)
