https://www.marthastewart.com/7976833/how-clean-blackened-aluminum-pan
Short answer is it's a combination of the detergent and the water that causes tarnish. I have aluminum pans that I use for baking, and they don't do this in my dishwasher, so it's either that the detergent you use is particularly alkaline, or that your water is "hard water", having more minerals in it than usual.
So the question is, what can a lazy motherfucker like myself do?
Ditch your aluminum cookware and get stainless steel stuff instead. Treat your dishwasher like the Thunderdome: anything that can't survive it is unworthy of your use.
It’s a good approach. But the aluminum I have is part of a whole. A rice cooker inner pot and a wok lid. Maybe I can find a replacement wok lid.
But what about knives? Dishwashers are said to dull knives. So far I only buy middle of the spectrum chef’s knives (~<$60) so abusing them isn’t a big deal. But that means I give up the benefit of a sharp knife that keeps a long-lasting edge. If I buy high-end (which likely runs a few hundred $), then it’s a bit wasteful to abuse it in the dishwasher. I suppose there are some things that I have to accept as high-maintenance. I wonder what pro chefs do.
So far only buy middle of the spectrum chef’s knives (~<$60) so abusing them isn’t a big deal.
Honestly, that's more than you need to spend. Get restaurant knives with tapered stamped stainless steel blades, e.g. Victorinox Fibrox. Cheap yet decent (recommended by America's Test Kitchen, Alton Brown, etc.) and NSF certified (which basically means dishwasher-safe even for heavy-duty commercial dishwashers).
That is just the aluminum oxidizing. Essentially rust for aluminum. It will happen no mater what with aluminum cookware unless it is anodized or coated in something. Even then it will still happen eventually. To be fair, the dishwasher is going to affect the appearance of even the most expensive pots and pans over time. It’s one of those things where you either accept it or put in the work (and waste the water) to keep it looking nice. The solution for me was buying stainless steel, throwing it in the dishwasher most of the time then hitting it with barkeeper’s friend every once in a while.
Aluminium-safe dishwasher detergents do exist, using sodium silicate, but they're damn expensive. Sadly you're better off cleaning aluminium cookware by hand.
That tarnish happens because aluminium is way more reactive than it looks like. It's amphoteric, so both acids and bases attack it. And, in a simplified way, soaps and dishwasher detergents tend to be basic enough to attack aluminium.
Typically this is not a big deal because there's a neat layer of aluminium oxide covering metallic aluminium (that's why it looks dull, instead of shiny). But if the aluminium or the solution are hot enough, that layer itself gets quickly corroded. And, well, dishwashers heat things up, right?
Weirdly enough I believe that the tarnish and white powder are also a mix of aluminium oxide and hydroxide. But since the tarnish isn't in a neat crystalline structure, but a porous one, it gets dark. You can remove that layer of oxide with some weak acid, like vinegar; the metal will regenerate a neater one.
Because uncoated aluminum is chemically sensitive. The staining won't impact performance but it is always recommended to hand wash aluminum.
There no way around being a lazy motherfucker here. Some things require more care.