Honestly the Flow isn't that strong for most fish. My Fx5 and Angels are perfectly fine and they have been in that tank for around 8 months. If you really want to slow it down, just pack tons of filter floss in the canister trays and that will lower you from 680 GPH to around 450 GPH.
125 Gallon Dirted/Fully Planted Community Tank
55 Gallon Amazon Tiger Barb Tank
29 Gallon CRS Shrimp Tank
20 Gallon Yellow Neo Tank
20 Gallon Half Moon Amazon Serpea Tank.
10 Gallon Blue Velvet Neo's
10 Gallon Betta/Cherry Neo Tank
10 Gallon Betta Tank
12G Rimless Club