There are lots of methods. The improtant stuff is make sure your water to add is properly prepared (correct temp and salinity) and aged (at least 12 hours or so).
turn off the pumps and then use a turkey baster and blast the rocks to free any detritus. Then change about 10% water using a gravel vacuum to help remove the top layer of detritus (or any algae/cyano
) that settled and creeps around the sand.
I then turn all the water circulation back on and then add the new water (just to help it mix quickly). I'm sure there is more you can do, but that is the jist of it...
Hope that helps.