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.
Beside Brightwell's ChaetoGro we have found two other fertiliser products which contain at least a very low percentage of Copper, which is Seachem Flourish Comprehensive and with a higher part of Copper but still lower than most other available Fertilisers TNC lite Aquarium Plant nutrient. Both are also Nitrate and Phosphate free.
For more heavier planted marine aquarium display tanks and planted refugiums it may be necessary to add Nitrate and/or Phosphate to maintain a recommended level of at least 3-5 ppm Nitrate and 0.01 ppm Phosphate, especially when using Brightwell Aquatics ChaetoGro, Seachem Flourish comprehensive or TNC lite.
Therefore, for low nutrient tanks TNC offers the TNC Complete Aquarium Plant nutrient fertiliser which includes Nitrate & Phosphate (but again this contains some Copper ).