The most important piece of equipment in a reef tank. A protein skimmer removes dissolved organic compounds before they break down into ammonia. I run an Aqua Medic DC Runner on my 90-gallon and it has pulled consistent dark skimmate for two years. Do not buy a cheap skimmer — a skimmer that overflows your sump at 2am is worse than no skimmer at all. I learned this the hard way.

The return pump moves water from your sump back to the display tank. Size it at 5 to 10 times your display tank volume per hour. DC pumps with adjustable flow are worth the extra cost — you can dial in the exact turnover rate your system needs without adding a ball valve to throttle an oversized AC pump.

Corals require specific light spectrums — primarily blue wavelengths between 420 and 480nm — to support their zooxanthellae. The AI Prime HD is the light I recommend for tanks up to 24 inches wide. I have grown Acropora frags to full colonies under it over 18 months. The intensity and spectrum are controllable through an app which lets you dial in the exact light schedule your corals respond to.

Corals need flow to bring food to their polyps and remove waste. Random flow patterns are better than laminar flow — corals that receive the same direction of flow continuously can develop flow shadows where polyps die. The Maxspect Gyre creates a cross-current pattern that has worked well in my 90-gallon without creating dead spots.

SPS corals consume alkalinity and calcium as they grow. You must replenish these elements continuously or your corals will stop calcifying and eventually die. Two-part dosing is easier to set up. A calcium reactor is more stable long-term. I switched from two-part to a calcium reactor after my first SPS colony and have not looked back.