You know you have enough filtration if your water tests results show Zero for ammonia and nitrite. Flow or circulation is a different issue, you want enough to keep debris suspended for your filters to pick it up, allow water movement in the tank and for good gas exchange and heat distribution evenly throughout the tank.
Nitrate levels are reduced through filter maintenance and water changes.
Do you test your tank water parameters yourself or do you have your Local Fish Store (LFS) do it for you?