A word of advice. Be very careful W/hatians; they move all over the place! My LFS warned me of this, but I bought them anyway. Three times I was awakened to a loud "sucking" sound. They had got caught in my powerheads, intake tubes, and my overflow. That next day...back they went to my LFS! Since they warned me about them, they would not give me credit, but that's ok...they were only 8 bucks each.