How to start your first reef tank

I’m rico, an engineer, and I’m planning my own first reef tank. The hardest part wasn’t the money — it was figuring out what to buy when every thread contradicted the last one. So I turned the buying decision into a system. This page is the front door to it: follow it top to bottom and you’ll go from “I want a reef tank” to a finished equipment list without having to reconcile ten conflicting forums yourself.

1. What equipment you actually need

A first reef runs on roughly nine things: the tank, a light, flow pumps, a heater (often a redundant pair), an auto-top-off, an RO/DI unit for clean water, test kits and salt. A protein skimmer joins the list only once you move past soft corals into a heavier bioload. Each piece has a sizing rule behind it — flow as a turnover multiple, light by target PAR for your coral type, heater wattage by volume and room temperature — and the pieces have to fit each other, not just the tank.

The full list, with the sizing math and where a skimmer does and doesn’t belong, lives in the pillar guide: the reef tank equipment list — what you actually need.

2. What it costs

Honestly? A first reef is a few thousand dollars of equipment, and the range is wide. A small 20-gallon soft-coral all-in-one can come together for around $925 in gear; a 120-gallon SPS system runs past $14,000. The gap is almost entirely the tank size and the coral difficulty you’re building for — bigger water and hungrier corals mean more light, more flow and a skimmer.

To put a real number on it, the site keeps a complete, verified $2,602 first-tank build — a 40-gallon all-in-one soft-coral setup, priced line by line against dated catalog data. To price your own size and coral type, use the reef tank cost calculator, which sums real reference prices into budget, mid and premium tiers.

3. AIO or sump — the first real fork

An all-in-one (AIO) hides its filtration in a back chamber; a sump moves it to a separate tank in the stand below. In spec terms it’s a trade between simplicity and headroom. The AIO removes plumbing decisions entirely — no overflow, no drilling, no return pump to size against head height — but the back chamber has limited room for a skimmer, heater and media, and less total water volume to buffer mistakes. A sump adds cost and plumbing, and pays that back with room to grow: a bigger skimmer, reactors, and a hidden place for heaters and probes.

For most first tanks, especially soft-coral and LPS builds, an AIO is the lower-risk start. Go sump-first if you already know you want a large skimmer or an SPS-heavy system — and if you do, size the skimmer to your sump before anything else, because footprint and rated water depth are where they fail to fit. That fit problem is covered in best protein skimmer by tank size.

4. See a real build, then generate your own

The fastest way to make this concrete is to look at a finished, priced system and then produce your own. Browse the sample builds to see complete equipment lists for real tank sizes, or answer five questions in the Builder and get a compatible list sized to your own tank, sump and budget — every pick explained, one honest total.

First-tank questions, answered

The questions I kept hitting while planning my own tank — answered short and honest, from the spec-and-price angle this site is built on.

How big should my first reef tank be?

Bigger tanks are more forgiving: more water dilutes a mistake, so temperature and chemistry drift slower. But cost scales with volume — a larger tank means a bigger light, more flow and more salt. For a first tank, a 20-to-40-gallon all-in-one is a reasonable sweet spot: enough water to stay stable, small enough that the equipment stays affordable.

Do I actually need a protein skimmer?

Not for a soft-coral first tank. On a small volume, regular water changes can handle nutrient export, and a skimmer is one more thing to size, fit and pay for. A skimmer earns its place once your bioload and coral demands rise toward a mixed or SPS system. The verified $2,602 40-gallon starter build on this site deliberately runs without one.

Should I buy reef equipment new or used?

It depends on what wears out. Pumps, powerheads, skimmers and heaters are mechanical and degrade with runtime, and used ones come with no warranty and unknown hours — a real gamble. Tanks, stands and sumps have little to wear and are much safer bought used. LEDs sit in between: check the age of the diodes and driver before trusting a used fixture.

What should I buy first, and what can wait?

Buy what the tank cannot run without first: the tank and stand, a light, a heater, flow, and a water source such as an RO/DI unit. An auto-top-off, a skimmer and dosing equipment can wait until the tank actually shows it needs them. Sequencing purchases this way spreads the cost and keeps you from buying gear you never end up using.

What are the real limits of an all-in-one (AIO) tank?

An AIO hides its filtration in a back chamber instead of a separate sump. That keeps setup simple, but the chamber has limited room for a skimmer, heater and media, and the smaller total water volume buffers changes less. It is a great format for a first soft or LPS tank, and constraining if you later want a large skimmer or a reactor.

Where do first-tank budgets blow up most?

On the parts people forget to budget for. Beyond the tank and pump, the RO/DI unit, salt, test kits, an auto-top-off and the stand quietly add up to a large share of the total. Lighting and flow are also where it is easiest to over-buy. Pricing the whole list up front, not just the obvious pieces, is what keeps the number honest.

How long before the tank is ready — what is cycling?

Cycling is establishing the bacteria that process ammonia into less harmful compounds. It is a water-chemistry milestone: you track it by testing until ammonia and nitrite read zero, which typically takes a few weeks. It is a matter of parameters and time — ReefRig speaks only to the equipment and the chemistry, not to what you should put in the tank afterward.

Can I trust one equipment list, or do I have to cross-check forums?

The conflicting-advice problem is exactly why ReefRig exists. Every pick in a build here is sized from published rules and priced against catalog data with a verification date attached, so you get one internally consistent list instead of ten threads that disagree. Treat it as a starting point you can check: every number traces to a stated source.