Temperature & Salinity: The Basics

Temperature and salinity are the two most fundamental parameters in reef keeping. Get these right, and you've built a solid foundation for your tank.

Temperature

Ideal Range: 76-80°F (24-27°C)

Most reef organisms originate from tropical waters with remarkably stable temperatures. Your goal is to replicate this stability.

Why Temperature Matters

• Metabolic rates - Higher temps = faster metabolism
• Oxygen levels - Warmer water holds less oxygen
• Disease resistance - Stress from temperature swings weakens immunity
• Coral bleaching - Prolonged high temps cause coral stress

Finding Your Target

Many reefers aim for 78°F as a safe middle ground. However, consider:

• Lower (76-77°F): Slower metabolism, potentially better disease resistance
• Higher (79-80°F): Faster growth, higher oxygen demand

Equipment Recommendations

Heaters:

• Use titanium or quality glass heaters
• Size: 3-5 watts per gallon
• Consider dual heaters for redundancy

Controllers:

• Apex, GHL, or similar for precise control
• Set alarms for temperature deviations
• Automate heater/chiller control

Avoiding Temperature Swings

• Keep tank away from windows and AC vents
• Use a chiller or fans in summer
• Float new water during water changes to match temp
• Never exceed 1-2°F change per hour

Salinity

Ideal Range: 1.024-1.026 SG (32-35 ppt)

Salinity measures the dissolved salt content in your water. This directly affects the osmoregulation of every organism in your tank.

Why Salinity Matters

• Osmoregulation - Fish and corals regulate internal fluids based on external salinity
• Coral function - Affects photosynthesis and calcification rates
• Invertebrate health - Snails, shrimp, and crabs are very sensitive
• Oxygen carrying capacity - Higher salinity = less dissolved oxygen

Measuring Salinity

Refractometer (Recommended)

• Most accurate for home use
• Requires calibration with 35ppt solution
• Temperature compensated models preferred

Digital Salinity Meter

• Expensive but very accurate
• Hanna, Milwaukee brands popular
• Requires periodic calibration

Hydrometer (Not Recommended)

• Cheap but inaccurate
• Air bubbles cause false readings
• Fine for fish-only, not for reefs

Managing Salinity

Evaporation

• Only water evaporates, salt stays behind
• Top off with fresh RO/DI water only
• Auto top-off (ATO) systems maintain stability

Water Changes

• Mix saltwater to match tank salinity
• Use RO/DI water for mixing
• Let saltwater mix for 24 hours before use

Common Mistakes

1. Topping off with saltwater - Raises salinity dangerously
2. Not calibrating refractometer - Leads to inaccurate readings
3. Large salinity swings - More than 0.002 SG change per day
4. Ignoring evaporation - Can concentrate salt quickly

Matching Natural Conditions

Natural reef water parameters:

• Temperature: 77-84°F (varies by location)
• Salinity: 35 ppt (1.026 SG)

Most successful reef keepers aim for 1.025-1.026 SG and 77-79°F.

Stability Tips

1. Invest in quality equipment - Cheap heaters fail
2. Use controllers - Automation prevents disasters
3. Monitor daily - Quick glance at temp/salinity
4. Keep a log - Track trends over time

Conclusion

Temperature and salinity are your tank's vital signs. Check them daily, maintain stability, and your livestock will thrive. These two parameters alone can make or break your reef.

Start logging your temperature and salinity with AQUAXONE →