Ah, some good advice Ari. Just something to add...
Hi Dude,
Normally when the fish is listless like you descibed it means it's already at last gasp stage. Terminal, so nothing you can do already except wait. [miracles do happen!]
The salt treatment is good to for fish as it promotes slime production, slows down some bacteria[kills at higher concentratiion] plus other numerous properties that help make your fish feel ok.
[at 1ppt. 100g -100liters is mild and some cories and tetras can take it]
It is normally better for you to put in your new fish into a QT[quarantine tank] so that spread of disease don't occur into your community tank.
A teeny bit more info on the
salt treatment and loaches/cories.
Not sure of your level of fishkeeping but it would be good to be as descriptive as possible in your question to avoid people dispensing wrong information. [Foruming is an art itself!]
For example if you imported wild angels from south america instead of buying it from the lfs[30-120 mins from your house] will mean a big difference in advice.
The fish from overseas typically would have a minimum of 48hrs in a bag of water that's saturated in ammonia and co2 with a low ph.[because of the ammonia] opening the bag means the co2 escapes and the ph goes up and the ammonia becomes the toxic form. The fish suffocates as it can't get oxygen.
So set up the QT beforehand and equalize the temperature open the bag and scoop the fellas right into the tank.
I've also tried dripping with thin airline hose from QT into new arrivals that were put into bucket. As soon as the water doubled, i scooped them into the QT.
A bit of homework beforehand needs to be done on your part regarding the water parameters that angels like.
So happy fishkeeping and hope the rest are doing better.
Regards
Stan