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Cultivating Macroalgae in Your Saltwater Aquarium

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Many saltwater aquarists cultivate certain species of macroalgae either in their main tanks, or in refugiums and sumps.

Macroalgae is sometimes called the "good kind of algae" as opposed to microalgae, (i.e. Hair Algae). Saltwater aquarists have found that a number of macroalgae species are very useful in their systems, providing food for the herbivores as well as reducing phosphates (PO4) and Nitrates (NO3) levels in their tanks. Some types of macroalgae also make excellent breeding grounds for copapods and amphipods, which are a staple food for certain fish and invertebrates kept in marine aquariums.

Purposes of Macroalgae

Ulva fasciata
Photo by Keoki Stender


Macroalgae cultivated in marine aquariums serves 3 different purposes: ornamental, nutrient (NO3, PO4) reduction and fish and invertebrate food.


Macroalgae Cultivated for Fish Food

  • Kelp on Rock, Smooth Leaf (Haliptilon sp.)
    • Color can vary from a dark pink to deep red.
    • Does not tolerate high NO3 or PO4 levels
    • Does best in moderate to strong lighting.
    • Best when grown in a refugium, rather than main tank.
  • Lettuce Algae Ulva (U. fasciata, U. expansa)
    • Readily accepted by herbivorous fish.
    • Removes both phosphate and nitrate from the water.
    • Use moderate to high lighting and keep it in an area of high water flow.

Macroalgae Cultivated for Food (cont.)

Red Algae (Gracilaria coronopifolia)
Photo by Keoki Stender
  • Limu Manauea (Gracilaria coronopifolia)
    • Endemic to Hawai'i.
    • Excellent surgeonfish food.
    • Remove ammonia, nitrates and phosphates from system water.
    • Does best in medium light.
    • Under the right conditions, biomass can increase 150% per month.

Nitrate (NO3) & Phosphate (PO4) Reducing Macroalgae

Chaetomorpha antennina
Photo by Keoki Stender
  • Shaving Brush Plant (Penicillus sp.)
    • Will benefit from the regular addition of an iron supplement, as well as trace elements.
    • Can go a long way towards helping reduce nitrate and phosphate from the water column.
  • Caulerpa
    • Must be pruned regularly to prevent rapid die-off during sexual reproduction which will pollute tank.
    • Can be found in various shapes, including flat blades, feather blades, notch leaf, and a grape-shaped variety.

Ornamental Macroalgae

Halimeda kanaloana
Photo by Keoki Stender
  • Shaving Brush Plant (Penicillus sp.)
    • Will benefit from the regular addition of an iron supplement, as well as trace elements.
    • Can go a long way towards helping reduce nitrate and phosphate from the water column.
  • Kelp on Rock, Smooth Leaf (Haliptilon sp.)
    • Color can vary from a dark pink to deep red.
    • Low nutrient plant.
    • Does best in moderate to strong lighting.
    • Best when grown in a refugium, rather than main tank.

Ornamental Macroalgae (cont)

Caulerpella ambigua
Photo by Keoki Stender
  • Maiden's Hair Plant (Chlorodesmis sp.)
    • Good breeding ground for amphipods & copepods.
      • Contains a toxic substance which deters herbivorous fish from eating it.
  • Mermaid's Fan Plant (Udotea sp.)
    • Do not tolerate high NO3 or PO4.
    • Require calcium
    • Caulerpa
      • Must be pruned regularly to prevent rapid die-off during sexual reproduction which will polute tank).
      • Can be found in various shapes, including flat blades, feather blades, notch leaf, and a grape-shaped variety.

Nutrients for Macroalgae

    • Some aglae require phosphates and nitrates to survive.
    • Some algae will not tolerate high nitrates of phosphates.
    • Calcareous macroalgae (i.e. Halameda) require calcium supplements.
    • Some macroalgae (i.e. Shaving Brush Plant) benefit from the regular addition of an iron supplement, as well as trace elements.

Sources for Macroalgae

Caulerpa webbiana
Photo by Keoki Stender

Sources for Amphipods

Amphipod Image
Photo by Stan Hauter

Without a doubt, your best (and least expensive) way to obtain some amphipods and copepods to seed your refugium with is from a friend's tank or from a friendly LFS. Most copepods and amphipods that show up in a marine aquarium have hitchhiked in on live rock. They are easy to collect from a filter and transport to your tank very well.

If you can not find amphipods or copepods locally, here are some which are commercially available.

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