I agree you need to be cautious what types of plants you use, they make a mess when they go assexual. I keep several types of plants in my tanks, I feel it is more for decoration than benefit. I have 5 large mangroves on a 58 gallon tank that are really cool, I took a CPR aqaufuge and hung it on the back of the tank just for the mangroves. it is a topic of interest for guests that see trees growing out of the tank. But honestly I feel it would take alot of mangroves to really make a noticable difference in water quality. the best thing for water quality is a good skimmer and water changes. as for caluerpa, it is also fun to play with and grow, it is probly a better nutrient export than the mangroves just due to the quick and lush growth. the more you cut and remove it the more you are removing nutrients from the water. I still am not sure that the typical refugium holds enough to help out. ideally you want alot of it to make a difference. I plan on having a 75 gallon tank strickly for caluerpa and mangroves on my next tank, and I dont know if that will help the tank or not.