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Saltwater Mix Calculator

Get the exact salt mix for your marine tank

Salt Mix Needed

5.0 cups

Weight

3.1 lbs

PPT

35

Salt Mix Needed

5.0 cups

1400g / 3.09 lbs

Target PPT

35

Mix Time

20 min

Mixing Tips

Use RODI water, heat to 78°F, add salt slowly while stirring with a powerhead.

Suggested heater: 30W for 10 gal mixing container.

What You'll Need

Zoo Med Turtle Clean 15 External Canister Filter

Zoo Med Turtle Clean 15 External Canister Filter

$47.954.7
View on Amazon
API Saltwater Master Test Kit 550-Test and Instant Ocean Sea Salt 50 gal for Saltwater Aquariums

API Saltwater Master Test Kit 550-Test and Instant Ocean Sea Salt 50 gal for Saltwater Aquariums

$57.364.6
View on Amazon
HITOP 100W Adjustable Aquarium Heater, Submersible Fish Tank Heater Thermostat with Suction Cups for 10-30Gal

HITOP 100W Adjustable Aquarium Heater, Submersible Fish Tank Heater Thermostat with Suction Cups for 10-30Gal

$15.974.1
View on Amazon
Zoo Med Turtle Clean 15 External Canister Filter

Zoo Med Turtle Clean 15 External Canister Filter

$47.954.7
View on Amazon
API Saltwater Master Test Kit 550-Test and Instant Ocean Sea Salt 50 gal for Saltwater Aquariums

API Saltwater Master Test Kit 550-Test and Instant Ocean Sea Salt 50 gal for Saltwater Aquariums

$57.364.6
View on Amazon
HITOP 100W Adjustable Aquarium Heater, Submersible Fish Tank Heater Thermostat with Suction Cups for 10-30Gal

HITOP 100W Adjustable Aquarium Heater, Submersible Fish Tank Heater Thermostat with Suction Cups for 10-30Gal

$15.974.1
View on Amazon

As an Amazon Associate, we earn from qualifying purchases.

Example Calculations

110-gallon water change at 1.025 SG

Inputs

Volume10 gallons
Target SG1.025
BrandInstant Ocean

Result

Salt Needed5.0 cups (1,400g)

10 gal × 0.5 cups/gal × (1.025 - 1.0)/0.025 = 5.0 cups. 5.0 × 280g = 1,400g.

250-gallon new tank setup

Inputs

Volume50 gallons
Target SG1.026
BrandRed Sea Coral Pro

Result

Salt Needed27.6 cups (7,718g)

50 × 0.53 × 1.04 = 27.6 cups. Weight: 27.6 × 280 = 7,718g (17.0 lbs).

Frequently Asked Questions

Q

How much salt mix per gallon of water?

Most salt mixes use about 1/2 cup (140g) per gallon to reach 1.025 specific gravity. Exact amounts vary by brand — always verify with a refractometer.

  • Instant Ocean: ~1/2 cup per gallon for 1.025 SG
  • Red Sea Coral Pro: ~0.53 cups per gallon
  • Always mix in RODI water, never tap water
  • Verify with refractometer before adding to tank
BrandCups/GallonTarget SGBest For
Instant Ocean0.501.025Fish-only, FOWLR
Red Sea Coral Pro0.531.025Reef tanks, SPS
Fritz RPM0.521.025Mixed reef
Q

What salinity should a reef tank be?

Most reef tanks target 1.025–1.026 specific gravity (35 ppt). Fish-only tanks can run 1.020–1.025. Consistency matters more than exact number.

  • Reef tank: 1.025–1.026 SG (35 ppt)
  • FOWLR: 1.023–1.025 SG
  • Fish-only: 1.020–1.025 SG
  • Keep salinity within ±0.001 SG day-to-day
Q

How long should I mix saltwater before use?

Mix for a minimum of 2 hours with a powerhead, ideally 24 hours. This allows salts to fully dissolve, pH to stabilize, and temperature to equalize.

  • Minimum: 2 hours with circulation pump
  • Ideal: 24 hours for full stabilization
  • Heat to 76–80°F during mixing
  • Aerate with air stone to raise pH
Q

Can I use tap water for saltwater mixing?

No. Tap water contains chlorine, chloramine, heavy metals, phosphates, and silicates that cause algae blooms and harm corals. Always use RODI (reverse osmosis deionized) water.

  • RODI water: 0 TDS, removes 95–99% of contaminants
  • Tap water TDS: 100–500+ ppm in most areas
  • Dechlorinator alone is NOT sufficient for reef tanks
  • RODI system costs $60–$200, pays for itself quickly

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Last Updated: Jun 11, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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