Macroalgae is a great tool for removing nitrates and phosphates from your marine aquarium’s water, but it only works if you trim it regularly. Because the plants take yo these nutrients as they grow, you lose or reduce that ability when you restrict growth, either because your run out of room or the algae starts to clump up and crowd itself out. Making the situation worse, if any part of the algae starts to die, say from being overshadowed, it will decompose and release those nutrients back into the water. So, trim your plants. It’s the only way to properly use a refugium for nutrient export.