It all kinda depends on what stock you're keeping. No such thing as too much filtration is true, but too much flow is definitely possible. You wouldn't want to put an fx6 on a ten gallon right? I have a 206 on my 36 gallon bow and the water is always pristine, but I also keep fish that don't like a lot of flow and I'm pretty under stocked. I also tried a 306 before the 206 and it was too strong, I had to limit the flow way down and doing that can cause premature wear and tear on the motor so I switched it out.