Originally Posted by thunderwaved
Is it ok if I give all of them some aquarium salt? If they don't have fin rot, will it do any harm?
No, a dose of up to 1 tsp of aquarium salt per gallon would not harm them. I used this on all of my bettas during their quarantine phase and they're all doing great. Just be sure to dissolve every little bit of the salt in warm, dechlorinated water before adding it to their tank - undissolved salt could burn them.
You may also want to consider ordering some Indian Almond Leaves (joshsfrogs.com has them) or Blackwater Extract. If you Google it, you would see that it's good for their general health because it naturally softens their water and strengthens their scales/fins. A high dosage will turn the water dark though.
Whatever you do, please don't let some pet store employee sell you Melafix - if you go to ultimatebettas.com, there's a thread there about how the key ingredient in Melafix is harmful to the labyrinth organ of anabantoids.