What are your ammonia, nitrite, nitrate, ph levels? Any ammonia or nitrite can kill. Sick fish need perfect water.
Maracyn 2 contains minocycline, a wide-spectrum antibiotic effective against gram-negative bacteria.
If it hasn't worked, I would check the water levels. If they are off, a 50% water change. You can dose again, also you can try another antibiotic, like erythromycin (effective against gram positive bacteria). You can dose both at the same time. You might consider an anti-fungal like fluconazole if you can find that at your lfs. Follow directions carefully so you don't overdose. I would also add fresh crushed garlic and some vitamins like Zoe to the food and water. I would only use aggressive treatment since your fish sounds pretty sick.
Continue hypo in qt. Use a refractometer to check the water accurately. Keep the tank bottom clean by vacuuming any debris while in qt. Water changes can be very helpful. Use aged, aerated salt water.
hth