I’ve obtained a sand sample from 1.5 inches down, rinsed the crud of it, added saltwater @ 0ppm, see what, if anything is released into the water after 24hrs, with occasional stirring. If anything glows I’ll refine the test hopefully with the helpful chaps on the chemistry forum. It’s unrinsed aragalive stuff also, that I used to help cycle the tank, along with as many other sources as I could lay my hands on at that time.I’m just curious how you test that? I use a Hanna for phosphate but obviously I’m testing a water sample. How do you test what’s in the sand? Genuinely curious.