What does everyone use to get the whitish residue out of the kettle. After about 10 batches it's starting to get noticeable. I have always rinse out kettle with water after I transfer the wort.
I usually hear people use bar keepers friend for tough beerstone when PBW doesn't cut it any more. I have pretty hard water, so even after cleaning everything I'll usually find white residue if I just leave the tap water to dry on its own.
Bar Keepers Friend is cheap and will make the bottom of your kettle shiny again. Alternatively, I've also used 1oz of StarSan per gallon of water. If it's just the very bottom of the kettle you can use just enough to cover the bottom, so say 1/2oz in a half gallon of water. Let it sit in the kettle for 30 minutes then dump it wipe the kettle bottom with a sponge while wearing a rubber glove, then rinse it out. Here's a thread of mine on the before and after doing this: https://www.homebrewtalk.com/forum/threads/removing-beer-stone-buildup-in-kettle.514868/
But I'd just pickup from Bar Keepers Friend. Be sure not to use it on any etched volume markings as it will fade them.
I make a thin BKF paste and work it with a stiff sponge - or a stainless-friendly scrubby for the really tough stuff.
That shiz will cut through almost anything...