How much aquarium salt do I need to use?

[Lyshymo]

So my poor Ozwald has came down with fin rot. His normally large, circular pectoral fins are now long, rectangular...so he definitely is missing some bits. They're "clean cut", but definitely weren't cause by anything inside the tank--they just started becoming transparent to what they are now.

I'm removing him from his 10g (he's been in there for only 2 days) and placing him in the 1.5g for awhile until he improves. Now the box says to add 1 teaspoon per gallon. Should I just use 1 teaspoon for now just to make sure it isn't overwhelming for him? Then I know people say to only use it 7-10 days so it doesn't start causing internal damage... I think since I've caught this early it'll clear up rather quickly so I'm turning toward using salt for about 3 days and then just doing a water change every 2 days to keep everything pristine.

Does that sound like a good plan (even for a start) or what would you recommend?

Also, a bit of details about him and the tank he'll be in.
Ozwald is still active and eating well. Nothing aside the missing "pieces" of his pectoral fins have changed.

The tank is, as stated, 1.5g and is heated (stays about 77-81 degrees), however it isn't filtered (has a filter, I just despise it as a black "powder" flies out of it and I don't trust that for my tank).

If you need more information, just ask!
And thank you for the help!(:

[sainthogan]

Fin rot is defined by jagged, red or black edges, not clean cut and transparent. It sounds more like he's torn them on something, and they are growing back. White or transparent fins are indications of new growth.
Was anything else affected? Are you absolutely sure there's nothing in his 10 gallon that could have caused it? What about fake plants, filter, rocks or decorations? Any tank mates? (Sorry, just trying to cover all bases)
I'm not sure about the salt treatment, I've never needed to use it on my fish. I would follow the directions, and see how he does. Watch him closely though, because some fish don't tolerate the aquarium salt very well at all.

[Sea Dragon]

I started using 1 tsp/gal and gradually increased the dose to 3 tsp/gal over the course of a week when my betta had fin rot. If you're sure he has fin rot, it won't hurt to just start with 1 tsp for 1.5 gal and gradually increasing the dose if the rot doesnt show signs of stopping or improvement

Edit: Oh and the black powder from your filter is probably just carbon, its what help cleans the water :) The powder should go away with use, rinsing the cartridge also helps.

[Lyshymo]

He has silk plants, no tank mates, and his body color has turned from his name blue/red to almost entirely white. The ends of his fins are "rough" looking...to me. And his fins definitely are not growing as the are smaller than what they were yesterday...yes they're long still but not round and literally look like rectangular fins. There isn't a single that that would've cause both of his fins to do the same exact thing. The places where his fins are missing, yes, are clean...but if something snagged them, they wouldn't be that clean. Something is definitely up though...and fin rot is as close as it gets (from searches I've done). :/