Which salt should I buy?

How reef salts differ, which one fits your tank, and how to mix it right. Includes our salt calculator.

All good reef salts make healthy seawater. The real differences are the calcium, magnesium and alkalinity they mix to, and whether they’re made for fish-only tanks or demanding corals. Pick one that matches how you run your tank, then stick with it so your parameters stay steady.

Not sure how much you need? Our salt calculator works it out for your tank size, with Fritz RPM preselected.

Open the salt calculator

What you’ll need

Fritz RPM Reef Pro Mix Sea Salt
Fritz RPM Reef Pro Mix Sea Salt

our default reef salt

From $25.34

Choose size
Fritz RPM High Alkalinity Sea Salt
Fritz RPM High Alkalinity Sea Salt

  • Fritz RPM High Alkalinity

    $64.34

    • Tropic Marin Pro-Reef Sea Salt
    Tropic Marin Pro-Reef Sea Salt

  • Tropic Marin Pro-Reef

    From $71.01

    Choose size
    • Tropic Marin Classic Sea Salt
    Tropic Marin Classic Sea Salt

  • Tropic Marin Classic

    From $67.58

    Choose size
    • Tropic Marin Bio-Actif Sea Salt
    Tropic Marin Bio-Actif Sea Salt

  • Tropic Marin Bio-Actif

    $135.46

    • D-D Seawater Refractometer w/ Auto Temperature Compensation

    Seawater refractometer

    D-D Seawater Refractometer w/ Auto Temperature Compensation

    or the Milwaukee MA887 digital

    $69.99

    How they compare (from the makers)

    • Fritz RPM Reef Pro Mix: at 35 ppt, Fritz lists calcium 400–450, magnesium 1300–1400 and alkalinity 8.0–9.0 dKH. A strong all-round reef salt.
    • Tropic Marin Classic: calcium 370–390, magnesium 1250–1300, alkalinity 9–10 dKH. Tropic Marin suggests it for fish-only and community reef tanks.
    • Tropic Marin Pro-Reef: calcium 430–450, magnesium 1300–1350, alkalinity 7–8 dKH. Tropic Marin suggests it for tanks that want higher calcium with lower alkalinity, such as those using a calcium reactor.
    • Tropic Marin Bio-Actif: calcium 430–450, magnesium 1300–1350, alkalinity 8–9 dKH, made for tanks using carbon dosing.

    Mixing, step by step

    1. Use clean water. Fritz recommends RO/DI water under 10 ppm TDS. Use a container used only for saltwater.
    2. Add salt to water. Never the other way round, and never add dry salt to a tank with livestock. Add it slowly while a pump circulates the water.
    3. Use the right amount. Fritz RPM: ½ cup per gallon (38 g per liter) for 35 ppt. Tropic Marin: 0.5 cup (about 140–150 g) per US gallon for 32–35 ppt. The salt calculator does the math for your volume.Fritz RPM Reef Pro Mix sea salt bagFritz RPM Reef Pro MixView product →
    4. Wait, then check. RPM mixes in about 15 minutes, and Fritz says alkalinity and pH settle about 2 hours after it dissolves. Tropic Marin is ready once the water is clear.
    5. Measure and adjust. Check salinity with a calibrated refractometer. Tropic Marin gives a specific gravity of 1.025–1.027 at 77°F. Adjust with a little salt or water, and heat to tank temperature before use.D-D seawater refractometerD-D Seawater RefractometerView product →

    Good habits

    • Buy a size that covers several water changes so your mix stays consistent.
    • Store salt sealed and dry.
    • Switching salts? Do it gradually over several water changes and keep testing alkalinity.

    Quick picks

    • New reef, mixed corals: Fritz RPM Reef Pro Mix or Tropic Marin Pro-Reef.
    • Fish-only or soft corals: Tropic Marin Classic.
    • Carbon dosing: Tropic Marin Bio-Actif.
    • Want higher alkalinity from water changes: Fritz RPM High Alkalinity.

    Whatever you choose, test alkalinity on the mixed water once in a while so you know what you’re adding with each change.

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