You can change up the way the tank filters but sumps are one of the easyier types of filtration IMO. Water overflows from the tank and falls into the sump. When it enters the sump, the water travels through various filter medias and then it is pupmed back into the tank. The pump in the sump determins your flow rate but you need to make sure the pump does not flow more water then your overflow can handle. You dont wat a pump moving 1500gph and an overflow that can only handle 1100gph...you'll empty the sump and overflow the tank. That pipe extending through the bottom of the tank should have a bulkhead fitting on it to seal that hole, if you dont have it you will need to find one. There is a DIY sump at the end of my tank build which is linked below.
