I installed my XP3 today. And leaving the Emperor 400 in. My reasoning is I'm eventually going to add another tank, and would like a fully cycled filter on it. It will probably be the XP3 that goes to the planted tank. Looking at another cheap 55G from Walmart for this, as I'm wanting to save for my big tank, which, depending on how much I can save, will be between 180G and 300G.