Adding a sand bed at a later time.....

[FishyFishy!]

I have been debating putting a sand bed back in my 131 FOWLR due to the fair amount of wrasses I have been accumulating as of late. Most of the species I am keeping like to have the sand bed to hide and sleep in. All of the wrasses seem extremely happy and are nice and healthy so far, but I hate to make them go against their instincts and not feel comfortable.

But my real question is, being a bare bottom since setup, how do I go about adding a sand bed without causing any mini-cycles or issues? The bottom of my tank seems to have a decent amount of algae and smaller chunks of rock etc etc. Will covering it produce die off?