What Nutrients does Marine Macro Algae need to grow?

Beside of sufficient light marine macro algae will just need a few major and minor nutrients to thrive in the marine aquarium well.
The amount they need will mainly vary with the amount of macro algae you use in your marine aquarium and how often you do saltwater changes plus what kind of livestock you keep in the aquarium.

Although marine macro algae 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).

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.

They will not thrive well in an environment without or very little Nitrate and Phosphate, or where additives are used as a Nitrate and Phosphate remover as these are the key nutrients macroalgae need to grow and survive. 
Please find at the end of this overview our recommendations for what water values your aquarium should have to keep marine 
macro algae in your aquarium.

Beside of the major nutrients Nitrate and  Phosphate they will need some minor nutrients like Iron, Sulfate, Biotin, Manganese and Iodine, which will normally be added with your regular water changes or can be added with separate trace element additions.

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.

Please note: 
The following list shows major and minor nutrients which macro algae will need to grow successfully in a marine aquarium. 
Always be careful on what and how much nutrients you dose into your marine aquarium, as it might harm fishes, invertebrates or corals when used not correctly. We can not take any responsibility for this!
If you have any questions or if you would like to know more about this please contact us.


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

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

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

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

Calcium is again another important element for the marine macro algae 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

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

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


Carbon

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 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:


Iron

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.

Iodine

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

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

This may be different for reef tanks or systems with a refugium ( sump ) macro algae setup.
As a general rule, this is for most macroalgae species we sell, but there will be some which will need a different environment.

If you are unsure please ask us before you order.

Temperature: Between 23-28 °C

PH: 7.9-8.2

Alkalinity: 8-8.3

Salinity: 1.024 - 1.025

Nitrate: Between 3-10 ppm

Phosphate: Below 1 ppm, good is 0,03 ppm

Magnesium: Around 1200 ppm - 1350 ppm

Calcium: Around 400 ppm - 450 ppm ( high levels are important for calcified species like Halimeda)

Iron: Around 0.01 ppm

Iodine: around 0.04 ppm