They really should write these dosages for smaller tanks. Okay, you'll need a container that holds at least 5 cups of dechlorinated water. Fill it up and add in the first dosage. Mix well. Now, add 1 and 3/4 cups of medicated water to his tank. The ratio is 1/2 cup of medicated water to one gallon of tank water. Change the water every day and redose the meds. If you can, you might want to put him in a small hospital tank to make the water changes easier.
I'm not sure, let's see how he does on the General Cure, if that helps his eye any. Otherwise I'd say yes, he probably would need the Maracyn Plus again.