I got 10 from mangroves.ca a year ago. I just stick the roots in the rocks just as long as yu keep the leaves outta the saltwater. I mist them with Rodi water in a spray bottle
My light isn't high enuff of the top of tank to use a syrofoam. As my mangroves are growing past the lights now and my light is a foot off the top of water level yu can put a dab of glue on a mangrove root and attach it to a rock if yu have no holes in rock at right heighth and the roots will grow around the rock
when I had my 93 gal cube I had them in over flow I hit them with a spray bottle every other day and they did amazing roots where big and helthy and I had no light on them