.6% Salt concentration for treatment for arowana and datnoid?

I'm currently trying to treat my arowana's tail problem.
currently my salt concentration is at .3%, which is 1.5 Kilograms of salt for my 150 gallon tank.
I'm planning to slowly bring it up to .6%.
anybody here has experience with this level of salt in their tank?
Can Arowana and Indo Datnoid tolerate the concentration?
at .3% , so far my aro or datnoid seem to be handling it pretty well.

thanks I don't think its ordinary fin rot.
I do 30% weekly water changes regularly.
There seems to be black pimple like stuff near the end of the tail and thread like stuff.
initially i thought it was parasites, have been trying to get rid of this for 2 years now.
i've also cleaned up my canister filter, my tank is bare buttom








So far after almost a week into .6% salt with Furazan gold antibiotics.

here's the result.







thread like stuff seem to be gone? but the pimple like stuff are still there, so I'm worried it might come back, I'va maintained my .6% salt for almost 1 week. not sure how long i should maintain, any advise?

btw here's a picture of my fish