is the Caribsea Super Natural Tahitian Moon Substrate really reef safe?
 

I've had so many issues with my tank, SPs die within weeks, pH super low and many other issues that I've not had with my first tank.

The only difference is the sand... this one has this black sand and I am not sure if it may be leaching metals into the water...

Any experiences?

It should be. A lot of people have used it. You might have gotten a bad bag or two, though, or the problem might lie elsewhere. I'm trying to remember what's in it, but it's thought to be fine.

Yes. I am trying to resolve these mysteries... I think I will end up sending water sample to a lab for testing.