A few weeks ago I tried running gfo
on my 60g tank. I did not rinse it, kinda forgot and my tank was covered in brown gfo
particles for almost a week. I did a huge water change to get it out and it was fine. i didnt lose any fish or anything. GFO
will not kill your fish unless there was something in it. A drop in phosphates, even if very large will not kill fish. It might make corals unhappy for a bit but thats it. There has to be something we're missing.
Sorry for your losses, it happens to the best of us.