The published number is a benchmark
A catalog flow rate may be measured without the hose routing, filtration media, height differences and debris that affect a real installation. Treat it as a starting point rather than guaranteed circulation inside your particular tank.
Match flow to tank inhabitants
Some fish benefit from strong currents while others do better with gentler movement. Observe where debris collects, whether gas exchange is adequate, and how fish swim around the outlet. Flow adjustment and spray-bar placement may matter more than choosing the highest advertised number.
Know the maintenance trade-off
Long hoses, accessible valves, media baskets and replaceable seals determine how often a filter actually gets serviced. Before buying, measure cabinet clearance, check spare-parts availability, and plan how to stop water when disconnecting the system.
A quick buying worksheet
Note tank volume, stocking level, measured cabinet height, hose run, noise tolerance, and the available budget. Read owner manuals and return policies. Compare a canister to a hang-on-back or sponge setup if the maintenance requirements exceed what you want.