Setup path, stage 1
Plan a reef tank: size, budget and UK running costs
Decide the size, the style and where the tank will live before you buy anything. These three choices set your budget, your electricity bill and how forgiving the tank will be for years.
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What do you need for this stage?
- A tape measure and a rough plan of the room
- An idea of which fish and corals you want (it sets the minimum size)
- Your electricity unit rate from your bill, or the cap rate below
- A spreadsheet or notebook for the budget
What size of tank should a beginner start with?
Most guides steer beginners to the middle. A UK retailer suggests 150 to 300 litres and points out that a larger volume changes more slowly when something goes wrong. UK forum advice tends to say 100 to 200 litres for a first tank (typical, check).
Small tanks are not harder to look after, but they forgive less: a stuck heater, an empty top-off reservoir or a heavy feed shows up in hours rather than days, and it is easy to overstock them. Large tanks cost more to fill, light, heat and change water for.
Plan for growth too. Reef Builders reports that about a third of keepers upgrade within five years, so a light, return pump and test kits that would also suit the next tank are not wasted money.
Check the fish you want before you choose. Each fish page lists a minimum tank size in litres, for example the ocellaris clownfish and the yellow watchman goby. Tangs and angelfish need far more room than gobies and blennies.
Should I choose a sump or an all-in-one tank?
An all-in-one (AIO) tank hides the filter chambers, pump and heater behind a false wall at the back. BRS says it nearly always recommends one for beginners: it is quieter, smaller and has fewer jobs. A reef-ready tank drains through an overflow into a sump below, which holds more water and more kit, at the price of more plumbing, noise and maintenance.
| Item | All-in-one | Tank and sump |
|---|---|---|
| Best for | Under about 300 litres, first tanks, flats | Over about 300 litres, heavy stocking, keepers who want to add kit |
| Noise | Usually quiet | Overflow and drain noise to tune |
| Leak risk | One box of water | Bulkheads and pipes; the sump must hold what drains back when the pump stops |
| Room for kit | Limited; some built-in pumps are small | Skimmer, reactors, refugium, dosing |
| Methods it suits | Water changes, all-in-one dosing | Everything, including the Triton method, which assumes a sump with a refugium |
If you choose a sump, work out how much water drains back when the return pump stops, and leave that much empty space in the sump. We cover the test in stage 3.
Where should the tank go?
- Weight: water weighs about 1 kg per litre, so a 200 litre tank weighs well over 200 kg once rock, glass and stand are added. On a suspended wooden floor, put it against a load-bearing wall and ask a builder if in doubt.
- Heat and light: keep it out of direct sun and away from radiators, doors and draughts. Sun feeds algae and overheats tanks in a UK heatwave; a cold outside wall makes heaters work harder in winter.
- Power: you need several sockets near the tank, protected by a residual current device (RCD). Plan the cable route so every plug has a drip loop.
- Water: a route to carry or pipe RO/DI water and old salt water, and somewhere for an RO/DI unit with a drain.
- Access: room to reach the back and the sump, and a floor that will not be ruined by a splash.
How much does a reef tank cost to run in the UK?
Electricity is the biggest running cost. Under the Ofgem price cap from 1 October to 31 December 2026 the typical unit rate is 26.32p per kWh (taken from Ofgem's notice as summarised in search results; use the rate on your own bill if it differs). Older UK articles still use the 34p cap of 2022 and 2023, so their figures run high.
| Example tank | What we assumed | Per day | Per year | Per month |
|---|---|---|---|---|
| Nano all-in-one, 60 litres | Return pump 15 W, 24 h; One wavemaker 10 W, 24 h; LED 40 W at 75% for 9 h; Heater, average 25 W | 1.5 kWh | £141 | £12 |
| Mixed reef, 200 litres | Return pump 30 W, 24 h; Two wavemakers 15 W each, 24 h; Skimmer 15 W, 24 h; LED 100 W at 75% for 9 h; Heaters, average 60 W | 3.9 kWh | £376 | £31 |
| Tank and sump, 400 litres | Return pump 50 W, 24 h; Three wavemakers 15 W each, 24 h; Skimmer 25 W, 24 h; Two LEDs 100 W each at 75% for 9 h; Heaters, average 120 W | 7.1 kWh | £683 | £57 |
A quick check: a 50 watt device running all day uses 1.2 kWh, which is about £2.21 a week at the cap. Practical Fishkeeping worked the same 50 watts out at about £2.86 a week at the old 34p rate.
Then add salt (a 10% weekly water change on 200 litres uses about 1,040 litres of salt water a year), test kit refills, RO/DI filters and membrane, food, filter socks or fleece, and replacement pumps and heaters. We have not yet checked current UK shop prices against a dated source, so we do not quote a set-up price here. Work out your own electricity with the running cost calculator.
How much time will it take?
Expect a few minutes every day (look at every animal, check temperature, top-off and the skimmer cup) and an hour or two at the weekend for the water change, tests and glass cleaning. From empty tank to first corals takes about two to four months if you follow the test gates on this path. The first-year routine sets out the schedule.
What are the steps, in order?
- Pick your size band (nano under 100 litres, 100 to 300 litres, or over 300 litres) from the fish and corals you want.
- Choose all-in-one or tank and sump.
- Choose the spot: floor, wall, sockets on an RCD, away from sun and radiators.
- Write a one-off budget (tank, kit, rock, salt, test kits) and a yearly running budget (electricity, salt, tests, food, spares).
- Decide who will look after the tank when you are away.
Your checklist
Tick items as you go. Ticks are saved in this browser only and fill the depth gauge.
0 of 6 done for stage 1. Saved in this browser only.
What test must pass before moving on?
There is no water test yet. Move on when you can answer these without guessing:
- The tank volume in litres and the net water volume you expect after rock and sand (the tank volume calculator helps).
- The floor and stand can take the full weight.
- Your yearly electricity estimate at your own unit rate, written down.
- The sockets are protected by an RCD.
What are the common mistakes?
- Buying a tiny tank because it is cheaper, then finding it swings fast and fills up with two fish.
- Choosing fish after the tank, then finding the favourite needs twice the length.
- Budgeting for the kit but not the electricity, salt and test refills.
- A spot in the sun or beside a radiator.
- No RCD, or extension leads on the floor under the tank.
Where do sources disagree?
| Topic | What sources say | Our reading |
|---|---|---|
| Best first size |
| Under about 75 litres is possible but forgives less. 100 to 300 litres suits most first tanks. |
| Are nano tanks harder? |
| We side with the middle view. A nano needs an auto top-off and a heater controller even more than a big tank does. |
| Sump or all-in-one for a first tank |
| All-in-one under about 300 litres; a sump above that, or when you plan a method that needs one. |
See also: Reef keeping in the UK, Holidays and sitters.
Sources
- Charterhouse Aquatics, a beginner reef keeper’s shopping list
- Reef Builders, how to avoid beginner mistakes
- BRS, reef-ready or all-in-one tank
- BRS, The Triton Method explained
- Ofgem, energy price cap from 1 October to 31 December 2026
- Practical Fishkeeping, how to reduce electricity costs on a reef tank
- Practical Fishkeeping, beginner’s guide to reef tanks: choosing a marine aquarium
Figures from sources read as a search summary only are shown as typical figures: check them before you rely on them. Found a mistake? Tell us how to fix it.