Recommended flow rate is 6 to 10 times the volume of the tank in flow rate, e.g a 90 gallon would require 540 gal
/hour minimum. I have a AC
110 and a Emperor 400 in a 55 gal
Malawi tank. I also have 2 AC
50 powerheads and an AC
30 powerhead connected to a sponge filter with the output going through undergravel PVC
jets. My tank is overstocked with 18 Mbuna.