In a macroalgae reef tank or planted refugium /sump it can be necessary to add nutrients like nitrate & phosphate, Iron and other trace elements to keep macroalgae healthy and well growing, especially when the macroalgae growth is not satisfying, or dying off and very often in marine macroalgae dominated reef tanks. 

Dosing nutrients can be as well very helpful to stimulate macroalgae growth in generell.

Beside of the main nutrients macroalgae will need to grow ( nitrate, phosphate ), Potassium, Iodine and Iron will support the growth of marine macroalgae too and can be safely added to the marine aquarium, following the instructions provided.

If you like to know more about dosing macroalgae in a reef tank you can find more about  HERE

Livealgae UK offers as well a range of fertiliser and additives for an optimized macroalgae growth, which you can find HERE

Beware:
We do not recommend to use fertiliser for normal planted aquariums, as they are often produced to use in freshwater aquariums and often include ingredients which can be harmful to marine life like critters, livestock and corals, especially when Copper has been added to it.

There are some readily mixed fertilisers available which are safe to use as they are specifically formulated for marine tanks, like Brightwell's ChaetoGro and Continuum's Basis Chaeto Grow