Initially when I purchased the tank stand, filter, they all came with blue sand, and I purchased the white stones and soak that white little stones with running hot water for 15 minutes and soak them for 24 hours with sometimes running hot water, sometimez it does has some chemica to go out..
And I changed partial blue sand and put the new one for a week, and then gradually removed the old one... so that would help to let all bio things and bacteria sits and transfer to new graavel.