I have an Atman AT-3335 (400l/h) that is in working condition. However the tank that I'm intending to utilize it for happens to be at the bottom of a 2-tier Gex stand and henceforth, siting very close to ground level. I seriously doubt the canister can work by itself due to the lack of gravitational action.

Thus, I'm looking at using at external pump to drive water through the canister (which will be off) and hope to seek some advice and opinions.

1) What would be a good flow rate to use for the external pump? My tanks is 2x1 1 housing a single arrowhead puffer.

2) Since the canister will be off, is there a need to remove the impeller?

Many thanks in advance.