It looks like one of the Brightwell soils? The one people use
with shrimp a lot? But either way, if you cap it with two inches of sand whatever nutrients are in it should not leach into the water column. But I'm real new at this; there are some really cool videos on YouTube with Father Fish, who has been doing dirted tanks for like 50 years, and he has experience with a wide range of substrates and how to cap them, and he always answers questions in the comments. Good Luck!