I would move the tank so it is not in direct sunlight or get something to cover the backs and sides. There isn't very many things to combat algae in a brackish tank and direct sunlight will surely cause a lot of algae. Also if that live plant starts to die off remove quickly, it may cause an ammonia spike. Good water maintence is a must for all puffers. Nice tank though. You can add bumble goby's, they are a fine fish.