Update from the rep. Can anyone weigh in?
"I would be concerned with the high levels (0.2 – 0.8%) of Manganese in this product which could be toxic to fish if it’s leachable. The Galaxy Garnet material is a water filtration grade, and thus this would not be an issue. With the Galaxy Garnet, I do have some concerns with the Feldspar, which could harm some breeds of fish depending on origin, and tolerances. Have you any prior experience with using Garnet in Fish Tanks that would tell us otherwise? I would hate for you to harm any expensive breeds with these products. I would say that Galaxy Garnet is likely the safest, but we cannot guarantee that this will not harm your fish."