I tried every single Marc Wiess product out there, even all the f/w stuff. I emailed the company when I was with a store to see if I wanted to carry any of their line. I even had a few emails back and forth with Karen Wiess trying to get some answers. The test tank was a 37g reef, well filtered with a 150w HQI 10k halide.
I saw black powder trigger a feeding response, but most of the product did not end up on corals. It triggered the response, but I didn't notice any extra growth, color, or health from the corals. The only other product that did anything was Bactor Boost from the organic line. It did eliminate NH3, but left plenty of NO2 in a new s/w fish only a coworker of mine was cycling.
I pretty much got nothing out of the products. I'm just glad I didn't pay for them. None of the products came close to living up to the claims on the bottle. Just stick to basic water parameters and forget about miracle products.