I anodize aluminum and thoroughly rinsing the metal in between
steps is very important. I recently moved to Oregon and the city
water is very soft so I'm having a hard time getting the aluminum
clean. I can find plenty of products that soften water but is there
something I can use to harden it?
Normally, soft water is better at wetting, and thus cleaning, than
highly mineralized (hard) water. But if you're having problems, why
not just switch to actually clean water? Go to the grocery store and
buy either bottled distilled water, or get the store brand bottled
water that comes from the dispensere, where you buy an empty
container and fill it yourself. Those machines use reverse osmosis to
filter the water, plus a carbon filter to remove traces remaining.
Unlike shelf brand bottled water, where minerals are often added
back in, those bulk dispensers do not, and the water is almost to the
standards of lab "deionized" water (Usually just called "DI").
Distilled will be slightly lower in dissolved minerals, but can
occasionally have higher levels of trace volatile organic compounds,
sometimes just leached from the bottles as it sits on the store
shelf. But for this use, the differences between distilled and the
bulk bottled drinking water will be pretty much negligable. And the
bulk bottled water is probably a good deal cheaper, especially since
you reuse the containers when you need a refill.