Tube sand is a low-quality sand that is in a tube type of bag. It is mainly used to weigh down the back of a pick-up truck in regions that have snow. It is also used to add traction when you get stuck on ice or snow.
Update:
I just checked with my store & the tube sand they provide isn't a good quality for aquariums. It's not been sterilized. I'll just wait for my local pool supply store (American Sale) to get pool sand back in stock.
like excuzzzeme explained, the tube sand is like a regular play sand. The stuff I saw at the store was kind of on the dirty side, so I won't be using it.
I've had Quickrete in my tank for almost 2 years now. No ill effects at all.
I do have pool filter sand in a smaller tank and think I would like to pull the Quickrete out and replace it with pool filter sand in the near future.
Its just a PITA to get all the smaller particles out and after pulling or rearranging plants there is a lot of small particles floating and landing on the plants and it looks bad.
So quickrete is safe, just would do pool if I had to do over.