Setup guide

30 Gallon Reef Tank: Setup, Gear List & Cost

Thirty gallons is the line where a reef stops being a nano. Below it, evaporation and one missed feeding can swing your chemistry in an afternoon; at 30, you finally get enough water to make mistakes in. Here's how to build one properly — including the honest question of whether you should run a sump at all.

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Why 30 is the smallest forgiving size

Stability scales with volume. In a 10-gallon nano, a day of heavy evaporation is a measurable salinity spike; in a 30, the same day barely moves the needle. Whether it's the classic 29 (30×12×18″), a "30 breeder," or a 32-gallon AIO cube, this size holds parameters steady enough that a working adult can keep a healthy reef without checking it twice a day. It's also the cheapest entry that doesn't fight you.

Sump or no sump — the honest answer

At this size, no sump is a legitimate choice. All-in-one tanks (rear-chamber filtration) and hang-on-back skimmers carry a 30 comfortably at typical stocking. A sump still wins on equipment-hiding and added volume — but it roughly doubles the plumbing complexity for a tank this small. If this is your first reef, an AIO or HOB build is the version you'll actually finish.

Know your real volume first

After rock, sand, and the air gap, a "30" usually sees water in the low-to-mid 20s — which changes every dose you'll ever calculate. → Get your true water volume (the 29 is a preset; AIO rear chambers count as sump volume).

The core gear list

Skimmer (or skimmerless)

A 30 with a light fish load can genuinely run skimmerless on water changes alone — that's not a compromise, it's how most nano-adjacent reefs run. If you stock normally, a compact HOB or AIO-chamber skimmer earns its keep:

→ Check which skimmers honestly fit a 30 at your bioload

See our full protein skimmer rankings →

Lighting

The one place a 30 is genuinely cheap: one quality fixture covers it. A 24–36″ footprint under 18″ of water means even mid-range LEDs deliver SPS-capable light at the sand. Pick from the fixtures with verified PAR data and spend the savings on the light you actually want.

Flow

Target 20–40× turnover — 600–1,200 GPH total — which one well-placed small powerhead (plus the return) usually covers. In 12 inches of width, aim flow along the length, never straight at the rock. Work out your target →

Heat

100–150W on an external controller. In a small volume a stuck-on heater cooks the tank fast — the controller isn't optional at this size, it's the cheapest insurance in the hobby. Size it for your room →

Rock + sand

20–30 lb of rock scaped open, ~30 lb of sand for a 1–1.5″ bed. Resist filling it — negative space is what makes small tanks read as mature instead of cramped.

What a 30 build actually costs

The two honest columns, 2026 US prices. The RODI line is the flex point: many 30-gallon keepers start on purchased LFS water (a 30 only drinks a few gallons a week) and buy the RODI unit later. Itemize your own tier with the build cost calculator.

Ranges, not quotes. Salt is the recurring line — a 30 doing 15% weekly changes mixes ~19 gallons a month; the salt rankings show what that costs per brand, and the water change calculator plans the changes themselves.

Stocking a 30 — the short list

This is the discipline size. A clown pair, a royal gramma or firefish, one goby, maybe a small blenny — and that's a full 30. No tangs, no angels except perhaps a coral-safe pygmy, nothing that cruises. Corals are where a 30 shines instead: the whole tank is prime real estate under one good light.

The order of operations

Tank placed and level → saltwater in → aquascape → equipment on → cycle (2–6 weeks, test, be patient) → cleanup crew → fish over months, corals as the tank matures. Small tanks punish rushing more than big ones.

Other sizes

If you have 36 inches of stand and another $300, the 40 breeder buys the front-to-back depth this size lacks. The step after that is the 75 — the size most reefers wish they'd started at.