A Question Abt Sand

[cleekdaFish]

I want to take out half of my medium fine gravel and put in some sand substrate. Its for my cories to scavenge the bottom with ease and it would look better. But I already have fish in the tank, will I harm my fish if I do a minor redecoration? and will my bio wheels impeller have a problem from the small sand particles? I will keep the gravel under the bio filter , that way it wont suck up sand particles