Quick decision
| Choose an AIO when… | Choose a sump when… |
|---|---|
| You want fewer plumbing decisions, a compact installation and a coordinated package. | You want hidden equipment, more component choice and easier expansion. |
| You accept limited rear-chamber dimensions and tighter maintenance access. | You accept more setup work, cabinet-space demands and additional potential noise points. |
The trade-offs that matter
| Decision | Rear-chamber AIO | Cabinet sump |
|---|---|---|
| Footprint | Self-contained, but rear filtration reduces display depth. | Uses the cabinet below and needs safe plumbing access. |
| Equipment choice | Constrained by chamber dimensions and water levels. | Usually greater space and layout flexibility. |
| Setup | Fewer connections; included components may be coordinated. | Return plumbing, drain behaviour and operating level require planning. |
| Maintenance | Everything is close, but chambers can be cramped. | Equipment can be easier to reach if the cabinet is well designed. |
| Noise and failure points | Short water path, though lids, pumps and chambers can still resonate. | Drain, overflow, return and cabinet each add variables to tune. |
| Upgrade path | Best when you are comfortable with the ecosystem and chamber limits. | Best when future equipment flexibility matters. |
Measure before choosing
For an AIO, record each rear chamber’s width, depth, operating water level and access from above. For a sump, record cabinet openings—not just interior width—plus skimmer removal height, plumbing route, electrical separation and spare volume when the return pump stops.
Cost is about completeness
A lower tank price can lose its advantage when it omits the return pump, heater or filtration hardware. See the concrete difference between current systems in the UK reef tank kit comparison, then model the full basket in the setup budget calculator.