Flow pattern plays a big factor in how much is too much. Generally, you want to see movement everywhere, no still areas. Some can achieve this with an appropriately sized filter, others need larger filters (best for heavier bio loads) and or powerheads to reach that goal. My 60 gallon cube has a total volume turnover of around 11.5x per hour and Ive been pleased with how it works with my current scape. I use powerheads in most of my tanks as my scapes would otherwise create dead zones. My 15 gallon column did great with 30x per hour turnover, all while not stressing my tetras, fish ,shrimp, or 20 species of plants including carpet sp... playing with water flow patterns in your tank is an art form in itself and what you decide on will be ultimately determined by what you wish to keep.