i did this several months ago to set-up an mbuna tank.
if you have good biological filtration in your filter you should not have too much of a problem.
if your gravel is naturally colored, you might consider leave a few handfuls in there--i think it makes for a nice effect with the sand.
go the lowes for your sand....get the medium coarse grain sand--50lbs for 2.39$ (its a steal)
if you run powerfilters, i would coever the intake pipe with a sponge and raise the pipe if possible.
sand grains WILL destroy your impeller if a fish "spits" a mouthful into your filter.
and please dont pee in my tank
M