FastAquatics
Step-by-step how-to

How to mix saltwater for your reef tank

Step-by-step protocol for mixing saltwater. RODI water + reef salt mix + aeration + temperature matching = stable reef parameters.

Beginner7 steps

What you'll need

Step-by-step

Step 1: Fill clean container with RODIUse a dedicated container - never one that held detergents or chemicals. Fill with RODI water (not tap, not bottled spring water).
Step 2: Heat to target tempAdd a small heater + powerhead. Heat to 78°F. Salt dissolves much faster in warm water.
Step 3: Add salt slowlyPour salt slowly into the moving water. Use approximately 0.5 cups (4 oz) per gallon for 1.025 SG. Use the salt-mix calculator at /calc/salt-mix/ for precise amounts by brand.
Step 4: Aerate 12-24 hoursRun powerhead constantly to fully dissolve and aerate the saltwater. CO2 dissipates during this time, raising pH to natural levels.
Step 5: Test salinityCalibrate refractometer with 35 ppt solution. Test mixed water - should read 1.025-1.026 SG. If low: add more salt. If high: add more RODI.
Step 6: Test temperature againMatch within 2°F of display tank before adding to the system. Cold water shocks coral.
Step 7: Use immediately or storeSalt water is ready to use. If storing: cap container, keep dark, use within 2 weeks. Long-term storage degrades trace elements.

Frequently asked questions

How long does saltwater take to mix?

12-24 hours with a powerhead. Adding salt + powerhead alone takes 1-2 hours to dissolve, but trace elements + pH stabilize over the full 24 hours.

Do I need RODI water for saltwater?

Yes, mandatory. Tap water has phosphate, copper, chloramines that fuel algae and kill coral. RODI = 0 TDS = predictable parameters.

Can I mix saltwater in the display tank?

NEVER for established systems with livestock. Salt creates massive pH/SG/temperature swings. Always mix in a separate container.

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Aquarium-keeping fundamentals

Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.

Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.

Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.

Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.

Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.

Frequently asked questions

How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.

What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.

How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.

Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.

Related resources

Saltwater livestock · Freshwater livestock · Coral catalog · Care library · Q&A library (222) · Glossary (127) · Disease database (50) · Calculators (29) · Interactive tools (7) · Husbandry deep-dives · DIY projects · State legality directory