Could either be flukes, protozoan parasite or fungus, hard to tell with your description and no pic. Your best approach would be to remove the copper treatment via water changes and fresh carbon every few hours since the copper is having no affect. Once done, then treat with hyposalinity and a broad spectrum anti biotic for gram negative bacteria. The two treatments combined are very safe when administered properly and will help eliminate the guess work of trying to treat an unknown.
Without a positive ID
on the problem it will be much harder to determine an accurate treatment. I am hesitant to mention this but if the above suggestion is not effective you may also need to try formalin dips but I would first see if the hypo/anti-biotic works first.
Is the "bubbley" stuff smooth, stringy or fluffy?
How is the fishs' appetite and breathing?