I only now use melafix, along with pimafix if there are open wounds. If this was my fish I would treat with aquarium salt ( 1 tablespoon per 10g) and do 33% or 50% water changes every day. Keep the temp up at about 85 degrees. If there was no improvement within 5 days then I would consider other treatment.
You also should add an airstone, oxygen content is lower in warmer water.