I have posted a few times about how I do water changes. All of my cichlid tanks, except my quarantine and hospital tanks, contain sand substrates. As a result, I use a system I created using Python water changers that easily minimizes loss of source water, cichlid fry, and sand. My process utilizes two Python brand water changing hoses and a few other components.
How do you remove a sand substrate from a tank, which contains fish, without stirring things up? One of the simplest ways is to use a gravity siphon.