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The Coral Ranch Guillard's F/2 Fertilizer, 12 fl oz bottle
Phytoplankton Culture

Guillard's F/2 Formula Microalgae Fertilizer Concentrate

The academic-standard recipe for growing your own phytoplankton, mixed and ready to use.

Choose your size

Prices as listed on Amazon on October 3, 2026. The current price on Amazon may vary.

  • Proven Guillard's F/2 recipe. The standard for marine microalgae culture since 1962, in a single ready-to-use concentrate.
  • Easy dosing. 1 ml per liter (about 4 ml per US gallon) of freshly mixed seawater. That is it.
  • Made in the USA. Manufactured in-house by The Coral Ranch, in a sealed, dropper-friendly bottle.

About this product

Grow your own live phytoplankton. Our F/2 concentrate supplies the nutrients, vitamins and trace elements that marine microalgae need to reach high-density cultures, using Guillard's proven formula.

Use it to culture Nannochloropsis, Tetraselmis, Isochrysis and other marine microalgae: live food for copepods, rotifers and brine shrimp, and for SPS corals, clams and larval marine fish.

Macro and trace nutrients come combined in one bottle. Just dilute with seawater, with no measuring of separate parts.

Why phytoplankton matters in a reef tank →

How far a bottle goes

8 fl oz (236 ml)
≈ 236 L / 59 gal of culture
12 fl oz (350 ml)
≈ 350 L / 87 gal of culture
16.9 fl oz (500 ml)
≈ 500 L / 125 gal of culture

Directions & care

Directions
Add 1 ml per liter (about 4 ml per US gallon) of freshly mixed saltwater to reach standard F/2 concentration. Shake well before use.
Storage
Store in a cool, dry place away from direct sunlight.
Ingredients
Sodium nitrate, calcium carbonate, monosodium phosphate, trace metal solution, vitamin solution.
Warning
Not for human consumption. Keep out of reach of children and pets. Avoid contact with eyes and skin; if contact occurs, rinse thoroughly with water. If ingested, seek medical attention.

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