99.9% will tolerate copper quite well. I recommend copper power and as long as they aren’t actively showing velvet or ich you can ramp it up slowly. You want to shoot for 2.0ppm now.
After my inquiry about irradicating ich vs controlling it, copper was on my to do list but I haven't gotten it yet as I wasn't planning on any new additions until tonight.After you do the freshwater dip, a bath in the API fungus cure (in a separate bucket) is an excellent idea. After they have a little time to recover, (and pending the results of the dip) you can decide on the next course of action...
Do you have copper or CP? Just in case...