Three labels, three different meanings
Manufacturers do not all publish the same flow measurement. Pump output is a pump rating; filter circulation describes the maker’s filter-system figure; maximum flow may use another stated condition. A column labeled only “GPH” can conceal these differences.
Our comparison keeps all three fields separate. An absent circulation figure stays “Not specified”; the maximum-flow figure does not silently take its place.
A real example: Fluval 107 and 307
Fluval lists the 107 with 145 GPH pump output and 95 GPH filter circulation. For the 307, the figures are 303 and 206 GPH. Selecting the larger number would make either filter appear to move more water through its filter system than the maker’s own circulation figure.
These are published ratings, not measurements taken in your aquarium. See the 107 record and 307 record for the corresponding model and manual.
Why your installation is another condition
Media loading, hose routing, lift, flow controls and accumulated debris can affect delivered flow. A specification is useful for comparison only when you retain its meaning and use the instructions for the actual installation.
Do not divide a nameplate flow by tank volume and treat that number as proof that all livestock will be well served. Flow tolerance, waste load, media and maintenance are separate questions.
Compare filters using the same flow measurement
- Choose the physical filter format that fits the tank and service space.
- Compare the same published flow metric where available.
- Check that there is room to install the filter and remove its media for cleaning.
- Use the exact product manual to check setup and flow adjustment.
If one model gives only pump output and another gives filter circulation, their numbers do not tell you which moves more water once installed.