Water temperature 78, ammonia 0ppm, nitrite and nitrate 0ppm and pH 6.8. filter fluval U3 and large sponge filter. Not over feeding fish eat all food before hits the bottom. Tank vacuumed monthly for my cycle levels. I've tried api clarifier and tetra clarifier. Tank has been set up for 5 months. Why won't my water clear up any ideas or solutions?