How to set up a saltwater tank (the honest 6-week plan)

If you're reading this, you're probably weeks away from buying gear, or you've already bought some and you're trying to figure out what comes next. Either is fine. The goal of this guide is to give you the shape of the entire project before you spend more money — because almost every expensive mistake in this hobby comes from doing the right step in the wrong order.

This is the canonical "start here" page. It links out to the specifics; treat it as the map.

Before you buy anything

Pick a size. 20–40 gallons is the sweet spot for a first tank. Smaller is harder, not easier — small volumes swing fast when something goes wrong. Bigger is forgiving but expensive. Don't start with a 10-gallon "to test the hobby." Test the hobby on a 30.

Pick a spot. It needs to be near a power outlet, away from direct sunlight, on something rated to hold the weight (a full reef tank is roughly 10 lbs per gallon — a 40-gallon system on a cheap cabinet is a flood waiting to happen).

Set a budget. A reasonable first reef tank, all-in, lands between $800–$2,000 for the system before livestock. Cut corners on the rock, the salt, or the sand and you'll be replacing them anyway. Cut corners on the controller, dosing pumps, or skimmer and you'll be fine — those are month-six problems.

Decide what you want to keep. Fish-only is the cheapest path. A soft-coral / LPS reef is the most beginner-friendly. SPS-dominant tanks need years of stability before they're realistic. Plan your equipment around the eventual tank, not the day-one tank — see our coral care primer if you're not sure yet.

Week 1 — buy gear and dry-fit

You're not putting any water in yet. You're getting everything in one place and confirming it fits.

Order the must-haves all at once so they arrive together: tank, stand, sump (if applicable), light, heater, powerhead(s), return pump, RO/DI unit, refractometer, salt mix, sand, and dry or live rock. Skip the protein skimmer for now if budget is tight; it can come in month two. The exact picks are in equipment essentials — and the specific brands we'd buy are on the equipment page.

Dry-fit everything on the stand before plumbing or filling. Confirm the light reaches the corners, the heater fits where you can hide it, and the return plumbing doesn't fight the aquascape you want.

Week 1 (continued) — fill, aquascape, run

1. Make RO/DI water to ~0 TDS and mix to 1.025 specific gravity. Don't trust a hydrometer — use a refractometer.
2. Add sand, then build the aquascape with the rock dry, on the empty sand bed. Glue or epoxy where needed. Plan flow paths, not just looks — see aquascaping fundamentals.
3. Fill slowly to avoid kicking up the sandbed. Use a plate or your hand to break the stream.
4. Power on: heater, powerheads, return, light. Set the heater to 78°F. Run lights on a basic schedule (ramp up over 1 hour, peak 6 hours, ramp down 1 hour) — full spectrum settings are fine to dial in later.
5. Let it run cloudy for 24 hours. It will clear.

Weeks 2–5 — cycling

This is where most beginners blow up their first tank. Cycling is the bacterial colonization step that lets your rock and sand convert ammonia into nitrate. Skip it or rush it and the first fish dies.

The honest timeline is 3–6 weeks, no shortcuts. Add an ammonia source (pure ammonium chloride dosed to 2 ppm, or a piece of raw shrimp), test daily, and wait for both ammonia and nitrite to read zero within 24 hours of dosing. Full method, common mistakes, and what to test for is in cycling a saltwater tank.

While the tank cycles, learn the chemistry. You don't need to test calcium or alkalinity yet — those matter once corals arrive — but water chemistry basics covers what each parameter does and why hobbyists obsess over them.

Week 5 — prepare for livestock

Once cycle verification passes:

• Set up a quarantine tank. A 10-gallon with a sponge filter (pre-seeded in the display sump for two weeks) is enough. New fish go here for 4 weeks of observation and prophylactic treatment before they ever touch the display. The reasons and the protocols are in quarantine and fish health — skipping QT is the second most common way beginners crash their tank.
• Plan your first fish. Hardy, peaceful, low-bioload, captive-bred if possible. The shortlist and the why is in first fish picks.
• Don't shop yet. Look, plan, and confirm availability — but the fish goes in the QT, not the display, on day one.

Week 6 — first fish

Buy one fish (one — not three, not "a pair plus a cleaner shrimp"). Drip-acclimate or float-acclimate per the QT guide, then start the 4-week observation window. Treat prophylactically if you're going that route.

Your display tank stays empty of fish during this time. It's not boring — it's the period where the rock encrusts, coralline starts to spread, and you'll learn what the tank's flow patterns actually look like.

Month 2 onward — pacing

After the first fish clears QT and joins the display, wait 2 weeks before adding the next. The bacterial colony grows in response to bioload; rushing it causes ammonia spikes. Adding 1–2 small fish every 2 weeks is roughly the right pace for the first 3 months.

Once you're past month three with stable parameters:

• Add a cleanup crew — snails first, then a hermit or two, optionally a shrimp.
• Consider first corals. Start with soft corals and beginner LPS. Skip SPS until month 9–12 minimum.
• Start testing alkalinity weekly. That's the parameter corals are most sensitive to.

The mistakes that kill first tanks

In rough order of how often we see them:

1. Adding fish before the cycle finishes. Patience problem.
2. Skipping quarantine. Ich and velvet move from the LFS to your display, and once they're in your rock, you've started over.
3. Buying tap water in a hurry "just this once." It'll fight you for a year.
4. Stocking too fast. Three fish in week one means two dead fish in week three.
5. Using a hydrometer instead of a refractometer. Off by 0.003 SG is normal — and 0.003 SG matters.
6. Buying gear piecewise as problems arise instead of planning. Everything in this hobby compounds. The skimmer "fine for now" becomes the skimmer "undersized" in a year.

What to read next

In rough order, if you're at week zero:

• Equipment essentials — what to buy and what to skip
• Aquascaping fundamentals — flow and structure, not just looks
• Cycling a saltwater tank — the patient, no-shortcut version
• Water chemistry basics — what each parameter does
• Quarantine and fish health — why every fish goes through QT
• First fish picks — the shortlist
• Coral care primer — when you're ready for the next chapter

The hobby rewards patience more than it rewards money. Most of what kills first tanks isn't bad gear — it's good gear used in the wrong week.