The short decision
Choose a nano when available space is a hard limit, the shorter equipment list is valuable and you accept constrained chambers and lower water volume. Choose a larger system when equipment access, future options and more total water matter enough to justify the floor load, purchase cost and power.
| Decision | Nano: roughly 40–125L | Full-size: roughly 180–350L |
|---|---|---|
| Planning setup cost | About £650–£2,500 | About £2,200–£5,500+ |
| Example annual electricity | Roughly £100–£420 | Roughly £300–£750+ |
| Footprint | Fits more rooms; cabinet may still be essential | Requires floor, access and delivery planning |
| Equipment fit | Rear chambers and lids impose hard dimensional limits | More sump and cabinet choices, but more plumbing |
| Water volume | Smaller absolute changes can move temperature or salinity faster | More water provides greater thermal and dilution mass |
| Expansion | Upgrades often compete for the same chamber space | Usually more room for controllers, dosing, reservoirs and reactors |
| Maintenance reality | Less water to prepare, but tight access can slow routine work | Larger jobs and consumable quantities, often with better access |
The cost crossover
A premium 75–125L AIO can cost as much as an entry-level larger sump system because it bundles lighting, filtration, cabinet design and compact engineering. Compare finished baskets, not litres per pound. Use the setup budget calculator and electricity calculator with the exact shortlist.
Five constraints to measure at home
- Floor and filled weight: tank, cabinet, water, rock and equipment—not nominal litres alone.
- Access: doorways, stairs, cabinet openings and the height needed to remove equipment.
- Heat: room temperature and heater duty cycle affect annual cost.
- Noise location: a quiet bedroom constraint is different from a separate living space.
- Expansion appetite: decide whether a fixed compact ecosystem is a benefit or a future restriction.
Where to go next
If nano still fits, compare the current compact kits. If the architecture is unresolved, read AIO vs sump. For broader systems, use the UK tank-kit comparison.