So I am planning out a sump build and struggling trying to figure out how to support both ReefMat and socks interchangeably. Maybe I'm overthinking this beause I don't regularly dose lanthanum--only if I get lax on upkeep for a bit and phosphate gets out of whack--but when I do I have always removed regular socks and dosed into a 5 micron sock over several hours. It actually becomes several 5 micron socks over several hours as they become plugged. But then I am confident the lanthanum immediately bonds phosphate, never makes it through the sock and is immediately removed. My pre- and post-dosing phosphate tests using both Hanna and Red Sea confirm this. I also regularly do ICP testing and using this method lanthanum has never once been present. To those that dose lanthanum into the ReefMat, do you test before and after observing expected results? And do MS ICP tests reflected undetectable lanthanum?