A reef tank chiller keeps your water temperature below what your room, lighting, and equipment would otherwise produce, and in a reef tank, temperature control isn't optional for sensitive inhabitants. Most coral species, particularly SPS (small polyp stony) corals like Acropora, Montipora, and Stylophora, suffer measurably at temperatures above 82 to 84 degrees Fahrenheit. Prolonged exposure to high temperatures causes bleaching, tissue necrosis, and eventually death in high-end SPS collections. Whether you need a chiller depends on your room's ambient temperature, the heat output of your lighting, and the specific species you're keeping.

This guide covers the situations where a chiller is genuinely necessary for reef tanks, how to size one correctly, the best models for different system sizes, and the setup details that affect long-term performance and reliability.

Does Your Reef Tank Actually Need a Chiller?

Many reef hobbyists run successful tanks without a chiller by keeping their home air-conditioned and selecting lower-heat lighting. A well-dialed LED fixture like the Kessil A360X or Radion XR30 produces far less heat than metal halide or T5 fluorescent lighting, and in an air-conditioned room that stays below 76 degrees, the tank may hold 77 to 79 degrees without any active cooling.

You need a chiller if any of these situations apply:

Your room reaches 80+ degrees in summer. Even with efficient LEDs, a room at 82 degrees will push a reef tank above comfortable coral temperatures. Air conditioning the entire home is one solution; a chiller is another.

You're running high-intensity lighting. Metal halide fixtures (still used in some SPS systems for color rendering) can add 4 to 8 degrees of heat to a tank. Some hobbyists using T5 in large systems run 6 to 8 bulbs and see significant water temperature increases.

You're keeping SPS corals with tight temperature requirements. Acropora kept at consistent 77 to 79 degrees shows better growth and color than the same species fluctuating between 76 and 82. A chiller lets you hold a precise set point rather than hoping ambient conditions cooperate.

You're keeping cold-water or temperate species. Some NPS (non-photosynthetic) coral species and certain anemone species prefer 68 to 72 degrees, well below typical tropical reef temperatures. These require active cooling.

Chiller Sizing for Reef Tanks

Sizing a chiller correctly is the most important decision in this purchase. An undersized chiller runs at maximum capacity continuously, which shortens compressor life and still may not hold temperature on hot days.

The standard recommendation is to size a chiller for a tank 25 to 50 percent larger than your actual volume. This provides enough headroom for the compressor to cycle off periodically rather than running flat-out.

Also factor in: - Sump volume. A 90-gallon display tank with a 30-gallon sump is a 120-gallon system. Size for 120 gallons, not 90. - Ambient temperature. Most chiller ratings assume a 77-degree ambient room. In a warmer space (85+ degrees), the effective cooling capacity drops. Go up a size in those conditions. - Lighting heat. If running metal halide or high-wattage T5, add one size category to account for constant heat input.

Sizing Chart by Tank Volume

  • Up to 30 gallons: 1/15 to 1/10 HP (JBJ Arctica Nano, Coralife Aquachiller)
  • 30 to 65 gallons: 1/10 to 1/7 HP (JBJ Arctica 1/10, Teco TK500)
  • 65 to 130 gallons: 1/7 to 1/5 HP (JBJ Arctica 1/7, Teco TK1000, Coralife 1/5)
  • 130 to 250 gallons: 1/5 to 1/4 HP (Teco TC20, JBJ 1/4 HP)
  • 250+ gallons: 1/3 to 1/2 HP or multiple units (Teco TC35, Pacific Coast Imports 1/3 HP)

Best Reef Tank Chiller Models

JBJ Arctica Series remains the benchmark for mid-range reef chillers in the US market. The 1/10 HP handles 40 to 80 gallons depending on conditions, runs relatively quietly, and has a digital controller accurate to within 1 degree. Replacement parts are available. The full Arctica line runs from $250 (1/15 HP) to $550 (1/4 HP).

Teco TK and TC Series are Italian-designed units consistently rated for quiet operation and precise temperature control. The TK500 covers 26 to 45 gallons; the TK1000 handles 45 to 90 gallons. Teco's thermostat reads to 0.1 degrees Celsius, finer than most competing brands. Priced 15 to 25 percent above JBJ but with strong long-term reliability reports from reef hobbyists running them 8 to 10 years without compressor issues.

Coralife Aquachiller Plus offers a more affordable entry point at $220 to $300 for their 1/10 and 1/5 HP models. Slightly louder than JBJ and Teco under load, but functionally reliable. Good choice if budget is a constraint and the tank is in a location where chiller noise isn't an issue.

Pacific Coast Imports Prime Chiller is a less marketed but well-regarded option, particularly in larger HP ratings. The 1/3 HP and 1/2 HP models are popular in larger reef systems where they cost less than equivalent Teco models.

For full model comparisons with real-world performance data across different tank sizes and ambient temperatures, see our Best Aquarium Water Chiller guide.

Installation for Reef Tanks

Reef tank chiller installation differs slightly from freshwater setups because of the saltwater environment and the presence of sensitive livestock.

Tap the return line in the sump. The most common installation routes a spur from the return pump through the chiller and back into the sump before the water continues to the display tank. This avoids running chiller water lines near the display tank's livestock and keeps the installation clean and contained in the sump cabinet.

Use salt-safe materials. Vinyl tubing (not rubber), PVC fittings, and stainless steel hose clamps. Some rubber compounds off-gas in saltwater and affect water chemistry. If you're using a new chiller with rubber O-rings or gaskets internally, rinse it thoroughly with fresh RODI water before connecting it to the reef system.

Temperature probe placement. Place the chiller's return temperature probe in the sump return section, not in the reactor area or skimmer section. The probe should read the water temperature that's actually entering the display tank. Positioning it in a localized cooler or warmer pocket gives inaccurate readings.

Differential setting for reef tanks. SPS corals tolerate small temperature swings but prefer stability. Set the chiller differential (hysteresis) to 1 to 1.5 degrees. A 1-degree differential at a 78-degree set point means the chiller activates at 79 and shuts off at 78. This is tight enough to prevent meaningful temperature swings without causing excessive compressor cycling.

Cable management in the wet environment. Route power cables away from water surfaces and secure them above potential drip paths. The warm, humid environment inside a sump cabinet can degrade cable insulation over time.

Pairing a Chiller With a Heater for Year-Round Control

Reef tanks benefit from having both a chiller and a heater, even if the chiller rarely runs in cooler months. The ideal setup uses a controller (Neptune Apex, Hydros, or a standalone Inkbird ITC-306) to manage both:

  • Chiller set to activate at 1 degree above target
  • Heater set to activate at 1 degree below target

This creates a dead band of 2 degrees around your set point where neither device runs. If the chiller and heater are both connected to a controller that monitors tank temperature independently, you gain protection against stuck-on failures from either device.

See the Best Chiller for Aquarium guide for more on pairing chillers with temperature controllers for fully automated management.

FAQ

What temperature should I keep a reef tank? Most reef hobbyists target 76 to 80 degrees Fahrenheit as the safe range. SPS-dominant tanks are often kept at 77 to 78 degrees for best growth and color. Mixed reef tanks with LPS and soft corals tolerate 78 to 80 degrees comfortably. Brief excursions to 82 degrees are usually not catastrophic; sustained temperatures above 84 degrees cause coral bleaching in sensitive species.

Can I just run the air conditioning harder instead of buying a chiller? Yes, and many hobbyists do. Lowering the whole-home AC set point by 4 to 5 degrees during summer costs roughly $30 to $60 per month in extra electricity depending on home size and climate. A similarly sized chiller costs $10 to $20 per month to run. A chiller targeted at just the tank is usually the more efficient solution, but it depends on your specific situation.

Where should I place a reef tank chiller? Outside the main cabinet if possible, or in an adjacent space with good airflow. Chillers expel significant heat from the condenser. Running one inside a sealed cabinet raises the ambient temperature the condenser is fighting against, reducing efficiency and potentially causing overheating. Many hobbyists run the chiller in a garage or adjacent utility space with the water lines routed through the wall.

How do I prevent saltwater from damaging my chiller's internals? Quality reef chillers use heat exchangers made of titanium or coated copper to prevent corrosion in saltwater contact surfaces. Check the manufacturer specs before purchase. JBJ Arctica uses titanium heat exchangers in their reef-rated models. Keep the intake screen clear of detritus and avoid running the chiller dry, as even brief dry operation can damage the heat exchanger.

The Short Version

If your reef tank temperature regularly exceeds 80 degrees in summer, or if you're keeping temperature-sensitive SPS corals in a room without consistent air conditioning, a chiller is worth every dollar. Size it for a tank 25 to 50 percent larger than your actual water volume, choose from proven brands like JBJ Arctica or Teco, install it with proper ventilation and appropriate flow, and pair it with a heater and temperature controller for full year-round stability. That combination keeps your reef at a consistent temperature regardless of what's happening in the room around it.