Review on Seachem 67105330 Reef Plus 500Ml by Laurel Rohr

I use it and it's hard to say it actually does everything I can relate directly to this product. But my tank is healthy and all my corals are thriving. After using up my entire 500ml bottle, I ordered a 2 liter bottle. When the 2 liter bottle arrived there appears to be a layer of dark substance at the bottom. So I shook it very well, but now it contains normal liquid and some small black residue that doesn't mix back into the solution. It makes me think it's been on the shelf forever because it's not mixed well. I probably should have returned it, but I started using it before I realized it wasn't old. My 500ml bottle didn't have this problem.