Water change water change water change. It's probably too late to get him to monster proportions but shouldn't be too late to get him to gain 3-4 inches.
Try doing at least a 50% water change every week. I'd be surprise if you don't notice and improvement after a month or 2.
Try doing at least a 50% water change every week. I'd be surprise if you don't notice and improvement after a month or 2.