Every canister filter gets a score from 0 to 100% built from six factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Filters are grouped by the largest aquarium the maker rates them for (up to 75 gallons, 76 to 150 gallons, and over 150 gallons) and use the same scale in every group.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per gallon of rated aquarium | 25% |
| Media volume | media volume per 10 gallons of rated aquarium | 20% |
| Turnover | pump output against the rated aquarium size | 20% |
| Efficiency | pump output per watt | 10% |
| Features | primer, shutoff valves, pre-filter, flow control and built-in extras | 15% |
| Warranty | warranty length | 10% |
Where the numbers come from
Rated tank size, pump output, media volume, power draw, features and warranty come from the maker’s spec page or manual, or the maker’s own copy on a retail listing. Where the US figures (120 V, 60 Hz) are published, they are used. Where two of a maker’s own sources disagree on a figure, it is left out rather than guessed. Prices are checked at Amazon and the maker’s own store, and the lowest price at a store the page links to is used.
The factors
Value is the current price divided by the largest rated aquarium, in dollars per gallon, on a log scale, so halving the price always counts the same. $6 per gallon scores zero and $1 per gallon full marks.
Media volume is the volume the maker gives for its media space, per 10 gallons of rated aquarium: 0.15 L scores zero and 0.70 L full marks. Makers measure this differently. Fluval gives a “total chamber volume” for the 07 Series and a “biological volume” for the FX Series, while EHEIM and OASE give a “filter volume”. Each figure is used as published.
Turnover is the pump output in gallons per hour divided by the rated aquarium size: 1.5 times per hour scores zero and 5 times full marks. Makers rate pump output with no media or hoses fitted, so real flow is lower. A lower “filter circulation” figure, where a maker prints one, is shown on the product page but not scored.
Efficiency is pump output per watt of power draw: 6 gal/h per watt scores zero and 22 full marks. A canister runs around the clock, so a more efficient pump costs noticeably less to run over its life.
Features is 30% for a priming button or self-priming pump, 25% for shutoff valves or an aquastop, 15% for a separate pre-filter, 15% for adjustable flow, and 15% for a built-in extra: a UV sterilizer, heater or water-change valve.
Warranty is the maker’s base warranty: 1 year scores zero and 5 years full marks. An extra year offered for registering the product is noted but not scored.
What isn’t scored
Filter circulation, canister volume, pre-filter volume, number of baskets, maximum head height and release date are listed but not scored. Noise isn’t scored because no consistent independent measurements exist across these filters.
Missing data
Media volume is what most separates one canister from another, so a maker that doesn’t publish it gets no credit for it: that factor scores zero and the product page marks it as estimated. Warranty works the same way: a maker that doesn’t publish one gets no warranty counted, the same score as a one-year warranty, marked estimated. For any other figure that isn’t published, the factor gets the neutral middle score (50) and is marked estimated. Features score neutral only when none of them is published; a feature the maker doesn’t mention otherwise counts as absent.
Ties and discontinued models
Products are ranked by score within each group. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.