What equipment do I actually need to start a reef tank?

Short answer: Day-one essentials are a tank, heater, light, a way to make saltwater (RO/DI + salt mix), a refractometer, a test kit, a thermometer, a net, and at least one powerhead for flow. A protein skimmer, dosing pumps, a controller, and a refugium are all real upgrades — but they can wait; buying them before a heater or test kit is backwards.

The details

The corpus draws a clear line between what a tank needs running on day one and what can be added later as the tank (and your budget) matures:

Get on day one: tank, heater, light, RO/DI system (or purchased RO/DI water) + salt mix, refractometer, test kit, thermometer, net, at least one powerhead/circulation pump.

Can wait: protein skimmer, media reactors, auto top-off (ATO), dosing pumps, additional/upgraded powerheads or wavemakers, a controller (Apex-style), a refugium.

General buying advice repeated across the corpus: keep it simple, buy the right gear rather than fancy gear, spend more on the equipment you'll actually look at, budget roughly one piece per paycheck rather than blowing the whole budget up front, and keep a spare heater and utility pump on hand. Rough equipment tiers exist for planning a budget — a Budget Build runs roughly $500-1000, a Mid-Range Build $1000-3000, and a Premium Build $3000+, scaling from an AIO tank with filter socks and a basic light up to a full sump, skimmer, controller, and automated dosing/testing system.

The numbers

Common mistakes

• Buying a controller or reactor before a heater and test kit. Automation is worthless without the basics it's automating.
• Skipping RO/DI to save money upfront. It gets more expensive later, in dead livestock.
• No spare heater. A single point of failure on the one piece of gear most likely to crash the tank if it fails.

When to worry

• Normal: Starting minimal and upgrading gear incrementally over months — this is the standard, recommended path, not a compromise.
• Worry: No heater, no thermometer, or no test kit in the tank at all — you can't stabilize or verify anything without them.

What's next

Two things need dialing in next, in either order: temperature and the heater in temperature-and-heater-basics, and circulation in how-much-flow-do-i-need.