HOB vs Canister vs Sump: Which Filtration Architecture Wins

Every aquarium filters its water through one of three architectures: a box hanging on the back, a canister in the cabinet, or a second tank plumbed below. The hobby argues about them endlessly, but the truth is unusually tidy — each architecture wins a specific tank size and keeper profile, and most 'which filter' confusion dissolves once you see where the lines actually fall. Here's the honest comparison.

The three architectures in one minute

A hang-on-back (HOB) siphons water up from the tank, passes it through media in an external box on the rim, and waterfalls it back — simple, cheap, serviced in ninety seconds without tools. A canister moves the media to a sealed bucket in the cabinet, connected by hoses: several times the media volume, near-silent running, clean glass lines, and inline equipment options, at the cost of a more involved service ritual. A sump is a second tank below the display, fed by an overflow and returned by a pump — effectively unlimited equipment and media space, added water volume for stability, and total display cleanliness, at the cost of plumbing, drilled or overflow-boxed tanks, and real setup complexity.

Head to head

Where the HOB wins

Below roughly mid-size, the HOB's advantages compound: it costs least, services fastest (which means it actually gets serviced), and its simplicity leaves nothing to troubleshoot. Quality HOBs with real media baskets — the AquaClear and Tidal class from our nano filter guide — run shrimp tanks, betta setups, quarantine systems, and standard communities indefinitely. Its ceiling is equally clear: limited media volume caps the bioload it can carry, the waterfall return bothers some rooms, and nothing integrates with it. For fishrooms and multi-tank keepers, the HOB's serviceability at scale keeps it the working standard regardless of tank fashion.

Where the canister wins

The canister owns the middle of the hobby — the serious planted tank especially. Media volume several times an HOB's carries heavier stocking; silence suits living rooms; and the inline ecosystem (CO2 diffusion, heating, UV, spray bars) is why aquascaping standardized on it, as our canister guide details. It asks two disciplines in return: the monthly service has to actually happen (a neglected canister quietly becomes a nitrate factory), and the hoses and seals deserve the small attentions that prevent the category's rare but memorable failures. For freshwater displays from mid-size up, it's the default for good reason.

Where the sump wins

Saltwater, mostly — and any tank big enough that equipment sprawl becomes the problem. The sump's real product isn't filtration; it's space: room for a proper protein skimmer, reactors, refugium chambers, probes, dosing lines, and an ATO reservoir, all invisible below the display, plus the stability of meaningfully more total water volume. Surface skimming via overflow gives reefs the gas exchange they want, and topping equipment happens in a utility tank instead of the show. The costs are honest: drilled tanks or overflow boxes, plumbing to design and trust, pump sizing, and the flood-thinking (siphon breaks, return-chamber capacity) that reef keepers learn as a rite of passage. Almost no small freshwater tank needs one; almost every serious reef ends up with one.

The decision tree

• Small tanks and fishrooms: HOB (or the sponge filters that undercut even it — nano filter guide).
• Mid-size to large freshwater displays, planted work, CO2 tanks: canister, sized one up.
• Reef tanks beyond AIO scale, and very large systems of any water type: sump.
• Torn between two: the smaller architecture serviced religiously beats the larger one neglected — pick the one whose maintenance you'll actually do.

Bottom line

The architectures aren't rivals so much as size classes: HOB simplicity below, canister capacity in the middle, sump infrastructure above, with all-in-one tanks packaging sump logic into a rear chamber for the nano reef crowd. Match the architecture to the tank's size and mission, then spend your attention where it actually pays — on the service schedule, which decides more about water quality than any box, bucket, or basement tank ever will. And take comfort that the choice is rarely final: tanks migrate architectures all the time — the HOB community that graduates to a canister at the first rescape, the canister planted tank reborn as a sumped reef. The media and the bacteria move with you, the lessons transfer completely, and the filter question, like most equipment questions in this hobby, is only ever settled until the next tank.