Simply, the mangroves are a nutrient export, like a algae filter. But they don't function the same. Chaeto takes out nutrients faster and easier than mangroves. That is why most say mangroves are just for the look. But my look is getto most would say; I'm fine with that.
I find that mangroves like dirtier water than most give them, and they want more light than most want to give them, so most people don't have any luck with mangroves,, but I really like them. They surely take out nutrients. I just put all my skimmate for over a week from my sixty into my forty and the mangrove are most likely the thing taking that out of the water. But sure, they have help from the chaeto in the fuge.