ITs actually South Down Sand Tropical Play Sand. It's an aragonite based "play" sand sold on the east coast for use in sand boxes etc.
It costs about $3-5 a 50lb bag.
Very cheap, good, aragonite sand that makes a good substrate.
Unfortunately, it is not available very far west (someparts of Ohio I am told) unless someone has it shipped, which costs....
And the company that produces it has a very bad environmental record.
I just got my sand bed to 4-5 inches deep this very afternoon and it took 180pds to get here (90gallon tank) and about 9 mos because of cost - I added the last 50lbs today.
This was with
Carib Sea Special Grade - 40lb bag
2 bags of Natures ocean Live Sand from LFS 20lbs each
2 50lb buckets of E.S.V. OOlite Reef sand
Total - $170
As you can see, with South Down I could have spent $20 and spent the other $150 on Live Rock instead.