Sump is going to be a 30g long.

aggie - hadn't thought about running a T. That's a good idea! Also, didn't take into account the skimmer turnover. I'll be using a Euroreef custom 6-2 w/Sedra 5000.

Karin - Was the 640gph the max for the pump or was that the actual flow rate in your sump? I'd like to keep mine between 700-800 since the chiller seems to work more effeciently above 700gph. Have you measured your flow rate with the 5.0? How high (ft or meters) are you pumping the water? My main concern is the manufacturers seem to over estimate on their flow graphs.

Chris - no biopellets here. Still going to use the Hiatt for a while.

So far, I'm leaning towards using the 4.0. If the flow isn't enough for the chiller, then I can upgrade to the 5.0 before springtime, and just use the 4.0 on the Hiatt canister.