The only filter I have experience with is the filter that came with my 23 gallon National Geographic aquarium. I like it because during water changes I can just disassemble it, clean, then put it back together easily. I will be getting a 75 gallon aquarium for goldfish. I will most probably have white sand as the substrate. I have looked at Amazon and found a Marineland Penguin Power Filter. I was thinking og getting two 30 to 50 gallon 350 GPH. I also saw an Aquaflow Technology AEF-302 External Filter System, but it seems intimidating. Any thoughts on these choices?