What Is This Rock And Is It Safe For My Tank?

[ncguppy830]

Yea i really like it.

 

[Jebbwardo]

i am curently getting my water perfect my ph in 0.5 to high and dont have a clue what my ammonia, nitrite and nitrate are at but i am checking in 30 mins do you think i could leave doing a water change even if my tank has high nitrate as i have no fish and its food for plants isnt it?