order placed ... what have i done ...

thanks to smaller amounts of the ingredients costing drastically much more, I will now have ... an amount ...

guess i'll offer some packs to my parents and maybe neighbours for roughly the price of the ingredients, then it won't be as silly

I am wondering if it would have been a good idea to use distilled water or at least water that has gone through like a regular brita-style water filter? i think the original video just called for tap water, but of course tap water can have varying degrees of hardness based on where you are.

Water hardness only considers alkaline earth metals (Erdalkalimetalle in german) and not Alkali metals (Alkalimetalle in german). In tap water, there's mainly calcium and magnesium.
Sodium (Natrium) that's in the two salts used here are in the alkali metals.

Drinking water most commonly has Ca2+, Mg2+ and Na+ in it (in terms of Ions, so it stands to reason that depending on your local tap water, the amounts might be off?

But maybe since you're dropping so much salt in there that it can't take any more, it doesn't really matter? You can only really do it wrong by not putting enough, and that is signified by "no residue on the ground", and having a bit of residue on the ground is totally okay and acceptable ...