Probably chloroquine phosphate, although I've never used it on either species before so I cannot vouch for it's safety. But I see no reason why either fish should have a negative interaction.
Your other two options would be hyposalinity and tank transfer. Between those two, I would opt for TT. Just be careful when handling the lion.
I'm pretty sure I've killed lions before treating with copper; so you are right, that's a big no-no.