I dunno, that doesn't make sense to me.
Reef Rock 2.1 is manufactured by mixing reef substrate, that is a mixture of sand, coral pieces, shells and more, with a cement mixture.
I bet it just needs a curing period.
I just checked mine and it's .055 ppm
Yeah, it's definitely weird. Did you see the YouTube video I did when I tested the rock? Check it out. I scraped it.
I just did a 35/G water change and it went from 0.32 to 0.16
Tomorrow it will be back at 0.4 lol