my 150 til I had a power failure and lost everything had 2 #4's and a #2 in it. My Koran did bodysurfing on the current of the 4's and the puffer loved the #2 for anything. When I get my tank vback up and running they will be back inthere AGAIN and when I get my 300 I will be running 4#4'sw and 2 #2's in it for circulation.