Having no problems, I wouldn't sweat it. Its likely iron to assist in algae growth. It is refugium substrate meant to assist in that type of filtration. I think, iron will only release so much into the water as it isn't very soluble. Not like the nickel and vanadium I had in my sand, and not really toxic. Be careful using magnet cleaners near there, but I wouldnt worry.
Yes. I also have the Caribsea Miracle Mud in my cryptic refugium along with a 6lb bucket of the now discontinued Walt Smith Fiji Mud.
I think I want to start collecting mud and stuff from the coast. Check out what I found last weekend at our boat ramp.
Ulva macroalgae...