Yeah, most plants won't tolerate salt. Java fern and anacharis are fine with salt though. Daily water changes should keep the KH up and fresh water is your best friend as mentioned. Remove any dead plant matter.I just did a water change , took the plants out, and add salt. It seems like ever time I add salt my plants die.
It's good the angel is now is his own tank. Now you can add the salt no problem. Daily water changes as well to keep water pristine and dose salt for water removed.I have them in my sick tank now. I put the driftwood that has amazon sword on it I put it a different tank before I put the salt in it. In my main tank I have amazon swords on my heir last leg.