I have a friend who keeps fish like I do, has a couple of large tanks he even built a 55 gallon into his wall that he runs as a saltwater fish only tank. He told me he found this stuff caled coal slag that resembles black onxy sand...... he said he has used it for over a year in his tank and has had not problems with it. He said he still has some left. Would any of you take a chance on this?
