For an optimal macroalgae growth it is vital to maintain proper nutrient / mineral levels in the marine aquarium to ensure that the macro algae can effectively grow and remove unwanted nutrients from the marine water, as algae will with its growth take out the Nitrate and Phosphate for a more clean aquarium water environment.
All macroalgae species and especially the fast growing algae species Chaetomorpha and Caulerpa will need beside Nitrate and Phosphate some other so called major and minor minerals to maintain optimal growth conditions. You will find more information about the detailed minerals which macroalgae will need to grow well here.
But as macro algae will not just reduce Nitrate & Phosphate levels for a more clean water environment, algae will consume other minerals like Magnesium, Calcium and Potassium too which are important for other tank inhabitants like hard and soft corals. It is therefore important to replace those consumed minerals to maintain a stable water quality.
An easy solution to dose minerals are ready mixed multi-nutrient solutions ( aka fertiliser ) like ChaetoGro from Brightwell Aquatics, which is especially formulated to use in the marine aquarium as it is Nitrate & Phosphate free, plus it does not contain any Copper.
Unfortunately most available fertilisers for the planted aquarium are designed to use in freshwater aquariums and include Copper, as this is an important mineral for freshwater plants. But as macro algae are not plants they will not need copper to grow.
Therefore, for low nutrient tanks TNC offers the TNC Complete Aquarium Plant nutrient fertiliser which includes Nitrate & Phosphate (but again this contains some Copper ).