Aquarium Salt Mix Calculator
Created by: Ethan Brooks
Last updated:
Calculate the precise amount of marine aquarium salt needed to achieve your target salinity. Supports multiple salt brands and provides mixing instructions for water changes, new tank setup, and quarantine tanks.
Aquarium Salt Mix Calculator
AquariumCalculate the precise amount of marine salt needed for your target salinity
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What is a Salt Mix Calculator?
A Salt Mix Calculator determines the amount of marine aquarium salt needed to achieve your target salinity for a given volume of water. Accurate salt mixing is essential for maintaining proper water chemistry in marine and reef aquariums.
This calculator accounts for your preferred salt brand, target salinity, and water volume to provide precise measurements. Whether mixing water for a new tank, water changes, or adjusting salinity, accurate calculations prevent dangerous parameter swings.
Salt Mix Calculations
Basic Formula:
Salt (grams) = Volume (gallons) × Salt Rate (g/gal) × (Target SG - 1.000) / 0.025
Standard Mixing Rates:
• Most brands: 130-140 grams per gallon for 1.025 SG
• Approximately 1/2 cup per gallon (volume varies by brand)
• 35 grams per liter for natural seawater equivalent
Salinity Conversions:
• 1.025 SG = 35 ppt = 35 g/L = 3.5%
• Each 0.001 SG change ≈ 1.4 ppt
Proper Salt Mixing Process
Step 1: Fill container with RO/DI water at room temperature. Never use hot water - it can affect salt chemistry.
Step 2: Add calculated amount of salt while circulating water with a powerhead. Add salt slowly to prevent clumping.
Step 3: Heat water to match tank temperature (typically 76-80°F) using an aquarium heater.
Step 4: Mix for 4-24 hours with circulation and aeration. Check clarity - water should be crystal clear.
Step 5: Verify salinity with a calibrated refractometer at 77°F. Adjust if needed and remix.
Frequently Asked Questions
How much salt do I need per gallon of water?
Most marine salt mixes require approximately 1/2 cup (about 135 grams) per gallon to achieve natural seawater salinity of 1.025 SG (35 ppt). However, this varies by brand - always check manufacturer recommendations and measure with a refractometer rather than relying on cups alone.
What salinity should I target for a reef tank?
Most reef tanks thrive at 1.024-1.026 specific gravity (32-35 ppt). Natural seawater is 1.025 SG (35 ppt). Fish-only marine tanks can run slightly lower at 1.020-1.023 SG. Always match your tank's existing salinity when mixing new water.
Should I use RO/DI water or tap water for mixing salt?
Always use RO/DI (reverse osmosis/deionized) water for marine tanks. Tap water contains chlorine, chloramine, phosphates, silicates, and heavy metals that cause algae problems and harm invertebrates. RO/DI water ensures you're adding only the elements in your salt mix.
How long should I mix saltwater before using it?
Mix for at least 4-24 hours with a powerhead and heater. This ensures complete dissolution, proper oxygenation, and temperature matching. Some salts dissolve in 30 minutes, but precipitation and pH stabilization benefit from longer mixing. Never add freshly mixed water directly.
Why does my salt mix differently than the instructions say?
Salt absorbs moisture from air, affecting weight measurements. Water temperature affects dissolution and specific gravity readings. Different TDS levels in source water (even RO) can impact final salinity. Always verify with a calibrated refractometer at 77°F.
What's the difference between reef salt and regular marine salt?
Reef salts contain elevated levels of calcium (420-450 ppm), alkalinity (8-11 dKH), and magnesium (1350-1400 ppm) to support coral growth. Standard marine salts match natural seawater levels. Fish-only tanks can use either, but reef tanks benefit from reef-specific formulations.
Can I adjust salinity by adding salt to my tank?
Never add dry salt directly to an aquarium with livestock - it can burn and kill animals. To raise salinity, perform water changes with higher-salinity water. To lower salinity, perform water changes with lower-salinity water or add freshwater for top-offs.
How should I store marine salt mix?
Store in a cool, dry place in an airtight container. Salt readily absorbs moisture, which changes its concentration per scoop. Avoid storing in humid areas like garages. Properly stored salt lasts indefinitely, though some recommend using within 2-3 years.
Sources and References
- Bulk Reef Supply, "How to Mix Saltwater for Your Reef Tank", 2024
- ReefBuilders, "Understanding Marine Salt Mixes", 2024
- Tropic Marin, "Optimal Salinity for Reef Aquariums", Research Publication, 2024