What are you feeding it and how often? I give mine a piece of SeaVeggies soaked with garlic, selcon, and zoe every morning. Then they get fed a variety of things in the evening. All of them look great! Maybe a bit on the thick side.
Try soaking the nori or seaveggies in the garlic, selcon, and zoe and feed that to them. In a week or two, I bet it clears up.