I am not sure if 1 canister filter is going to be enough water movement for a 125...
The rule of thumb is anywhere between 5X and 10X the tank volume for FOWLR and between 10X and 20X for a reef system.
So for a 125 you would want:
625 GPH - 1250 GPH for FOWLR
1250 GPH - 2500 GPH for a reef system
Good Luck!