This is a strange filter. First the Canister has to be completely empty in order for it to prime correctly. Second The rubber gaskets between trays has to be seated good and tight ,you should almost feel the tray snap in place(I add some Vasaline very lightly to help make sure it seals good). Make sure tank is good and full with both intake and output well under water(I keep a extra bucket ready to pour in as this takes up some water) at no point do you want to let ither get above or even close to water leval. The instructions are crazy I dont remember but it says something stupid like press twice (it take way more then that just do it gently the output will start to bubble like crazy then it will realy start sucking water (make sure you are still not plugged in to electricty). When its full the bubbling will stop, at this point plug it in, it will spit air on and off for a good hour at times it may look like you have no output!!!. After about one hour gently tip the filter back and forth, than left and right it will start spitting air again with each tilt (which does not need to be tipped to far, a couple of inches maybe). This will bleed remaining air. At this point you are good to go. One tip, if you hear it getting a little bit load then you need to tip filter to bleed air. In the design the head will hold some air and not bleed it all by itself.
You need to almost go to school to learn how to restart this filter!!!! Once you get that one minor issue down it's a filtering beast.