What Nutrients does Marine Macro Algae need to grow?

Marine Macro Algae will need a few major and minor nutrients to thrive in the marine aquarium well. The amount they need will mainly vary with the number of macro algae you use in your marine aquarium, how often you do saltwater changes and what kind of livestock you keep in the aquarium.

Although marine macroalgae are not plants they will need almost the same essential elements like plants.
But as algae don't grow with roots, the nutrients must be supplied through the water and not through the substrate ( like Freshwater aquarium plants which can be fed by fertiliser through the substrate).

Macroalgae will need just a few major nutrients which will provide the basic needs for them to grow, and some minor nutrients along with them.

In a reef tank or marine aquarium setup with just a few macro algae species, it is normally not necessary to add any of the following nutrients to the marine water, as normal water exchanges and the present of livestock will provide enough nutrients for the macro algae to grow.

If the marine aquarium has a lot of macro algae in it, or if it is a planted marine tank it might be necessary to add some of the major and minor nutrients.

The following list shows major and minor nutrients which are needed for macro algae to grow successfully in the marine aquarium. Always be careful what and how much nutrients you dose into your marine aquarium, as it might harm fishes, invertebrates or corals.
We can't take any responsibility for this! If you have any questions or if you would like to know more about this please contact us.

For a macro algae tank we recommend the following guideline for the marine water chemistry:

This may be different for reef tanks or systems with a refugium
( sump ) macro algae setup.

Temperature: Between 23-30 ° C, we keep our tanks mainly around 26 °C

PH: 7.9-8.2

Salinity: 1.024 - 1.026. 

Nitrate: Between 5-10 ppm

Phosphate: Below 1 ppm

Magnesium: Around 1200 ppm - 1300 ppm

Calcium: Around 400 ppm - 450 ppm ( important for calcified species)

Iron: Around 0.01 ppm

Iodine: around 0.04 ppm

Main Nutrients

The main nutrients which are necessary for a good and healthy macro algae growth through photosynthesis are:
Nitrate, Phosphate, Magnesium, Potassium, Calcium, Sulphur and Carbon.


Nitrate is the major nutrient which is necessary for the macro algae to grow.
In the marine aquarium Nitrate if normally enough available, due to the nitrogen cycle and the fish waste. In fact, often the nitrate levels in marine tanks are so high, that it leads aquarists to think about the use of macro algae, whilst looking for a natural way to reduce the Nitrate level in the marine water.
In a marine aquarium with soft coral and/or fishes, it is normally not a problem to have a Nitrate Level between 5-10 ppm.
Whilst reef tank owners with hard corals will aim for a much lower nitrate level so that it is just available in traces.
Often macro algae will be used in that case just to keep the nitrate levels very low, which will cause a slower growth of the macro algae.

When your Nitrate Level is too low, which will be often just the case within heavily planted marine aquariums, like our main cultured macro algae tanks, you might need to add this nutrient to the water. We add regularly CaNO3 ( Calcium Nitrate ) to maintain a Nitrate Level of 5 ppm. Another way to add Nitrate would be KNO3(Potassium Nitrate).


Phosphorus is the second main nutrient for the macro algae growth.
In the marine aquarium, this is often enough available in the form of Phosphate PO4. Phosphate will be mainly introduced into the marine aquarium with fish food like flakes and especially frozen food blocks, but as well through detritus and fish waste.
Macro algae will need much less phosphate than Nitrate for its growth, therefore a Phosphate Level below 0.06 is enough to keep macro algae successful in the marine aquarium.
But even the often recommended Phosphate level around 0.03 ppm is enough for a marine aquarium with just a few macro algae in it.
This lower Phosphate level is recommended especially when hard corals are kept, as a higher level will negatively infect the coral growth.


Magnesium will be often sufficient enough available in the marine aquarium, as it will be replaced with saltwater changes.
In heavily planted marine tanks it might be necessary to add magnesium to maintain a Magnesium level around 1250-1350 ppm


Calcium is again another important element for the marine macroalgae growth. Especially calcareous macro algae species like from the Halimeda family will need a higher calcium level for its growth.
Unfortunately, calcium can't be easily added to the marine aquarium like other nutrients/elements, as the available calcium in the marine water depends and influences directly with the Alkalinity and PH Level of the marine water.
There are readily mixed solutions available which will keep that balance intact by increasing the Calcium level.
We use Calcium reactors to maintain a good calcium level of around 430 ppm.
Normally macro algae will be fine with a calcium level range between 380-450 ppm.
As mentioned before adding Calcium alone to the marine water will affect your PH and Alkalinity levels. For macro algae, it is recommended to keep the Alkalinity between 7-10 DKH, and the PH Level between 8-8,5.


Potassium is another important nutrient for the marine algae. It will be commonly sufficiently enough available in the marine water as it will be replaced by saltwater changes ( Please check the salt used, that it includes Potassium ).


Sulphur is normally sufficient enough available as it will be replaced with water changes.


Last but not least macro algae will need carbon for its growth, which will be turned into oxygen. Carbon will be sufficient enough available in the most marine aquarium and the produced oxygen will be helpful when the marine aquarium inhabits a lot of fishes.

Minor Nutrients

Beside of the Major Nutrients, marine macro algae will need some minor nutrients to allow a healthy growth and development.
Sometimes these nutrients are often referred to as trace elements.

As for Major Nutrients, it won't be necessary to add any of those Nutrients/Elements to a marine or reef aquarium with just a few macro algae in it. Just in heavily planted marine aquarium setups, it might be necessary to add some of them periodically.

We add to our algae tanks mainly the following minor nutrients:


Especially in heavily planted marine tanks, it might be necessary to add Iron. There are a few ready mixed Iron solutions available,
which are specially made for marine aquariums. Be careful with normal Iron Solutions, as they might include Nutrients/Elements, which can be harmful to the marine aquarium inhabitants.
We use Ferrion, which is a concentrated Iron supplement for all marine fish and reef aquaria.

There are ongoing discussions about what Iron level should be maintained. We have actually good experiences with an Iron level between 0.05-0,1 ppm.


Like with the supplement of Iron there are ongoing discussions about the benefits of adding Iodine to the water.
We actually add one drop per 100l every few days to our tanks and are happy with that. Especially Red and Brown Macro Algae species are believed to grow better with it. There is, unfortunately, no recommended Iodine level available.

Vitamin B12

Very rarely we add some Vitamin B12 to our tanks, and just in very low amounts, as we noticed micro algae bloom when too much get added.

Other minor Nutrients are as well necessary for the growth of macro algae, but they are normally sufficiently replaced by water changes.

These are:
Manganese, Copper, Molybdenum, Zinc and Boron

Livealgae UK - Premium Marine Macro Algae

Frequently Asked Questions

Do you have a shop to visit?

As an aquatic algae farm, we don't have a public shop to visit unfortunately but we are happy to post all our macro algae species within the UK for free to you.

And we are sure you will like your new macro algae addition once received.

How do I know when a algae is back in stock?

You can register your interest on the algae page you are looking for to get an email once it is back in stock or stay informed via our Newsletter, and or to follow us on Facebook, as we will first inform there when our algae are ready to sell again, or when we received new macro algae species.


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What means "Regrowing"?

When a macro algae species sells well we have sometimes to take it out of the sale as it will need time to regrow again.

The time for this will vary, as some macro algae species will grow very slow, whilst other - especially various  Caulerpa marine macro algae species grow quite fast.

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