How do I descale with citric acid vs commercial descaler?

Citric acid (food grade, ~$5/lb) is an effective, cheap descaler — use 1–2 tablespoons dissolved in 1 liter of water. Commercial descalers (Dezcal, Urnex) are formulated to be more thorough and leave no residue, making them slightly safer for machines with aluminum components. Both work well for most machines. Always run 2–3 full tanks of fresh water after descaling to flush residue. Check your machine's manual — some manufacturers void warranty if you use third-party descalers.