First what type of fish do you have in your tank and how many. That affects how much filtration your going to need. I love the rena xp3 filters but would not run them alone on a 75g tank. There flow rate is way overstated. My personal opinion is that if you have much bio load at all use a combo of your current HOB a penguin 350 (or emperor 400) and a rena xp3. I run multiple filters on all my tanks and its saved me more then once. Sounds like a lot of filtration but to me its not. Just my two cents.