Geberra, de-scaling is like removing the white white substances sticky onto the heating element.. if u use a electric kettle will also need to descale once a while. Coz i m using hand me down so sure will have it. Not sure how to use cirtic acid, but if use lemon, I just squeeze the lemon juice and mixed with water and let the sterlizer run like normal, ie On it with diluted lemon juice in it, afetr a cycle u will see the white substance coming out then just rinse away.
Maybe citric acid also work the same way, as in dilute it? Wait for lollypop to tell us... hehe