After having my Alexia for a little under 2 years, I decided to try descaling it today--my water is normally very soft, but in the summer/when reservoir levels get low, they mix in water from harder sources, so the exact hardness is changing all the time. Should still be fairly soft even when mixed, though.

The dezcal didn't really give specific instructions for espresso machines, so I googled around. This was very frustrating. The instructions I found here were for an HX machine. There was a reference to an "Insanely Long water FAQ" with a section on descaling, but that was a dead link. A lot of what I found elsewhere had conflicting info. Some had jargon or technical terms that were not explained and weren't clear if they applied to my machine. Eventually I followed the instructions at http://www.seattlecoffeegear.com/servic ... so-machine

They say to check your machine's user manual for specific instructions, but of course all the Alexia says is, "for liability reasons we're not going to tell you about descaling." The Seattle Coffee Gear instructions didn't specify how much dezcal to use, but I followed the packet instructions--1 envelope per quart of water, and since it's a 3 liter reservoir I stirred in 3 envelopes.

It all seemed to go alright, flushed it out a whole bunch, then for the heck of it I decided to drop some baking soda in the water I pulled through after flushing. From the group head it was fine, but from the steam wand, it fizzes no matter how much I run through the thing.

Can someone please tell me, in very simple terms and/or with whatever necessary explanatory links/diagrams/crayon cartoons what I did wrong, what I was supposed to do, and what to do now?

You probably need to flush more. The descaler would be an acid and baking soda is a base. Mix the two and you get the foam. Run another tank full of water through your steam boiler (sorry, not sure if Alexia has separate boilers/chambers for steam and brew).

When I descale my machine I run at least 4 boilers full of water through it to flush it out plus the heat exchanger.

You could always look in the FAQ. There are a couple descale how to's like this one.

Water, Scaling and Descaling with HX machines?

The Alexia is a SBDU (Edit: Single Boiler). I think you simply need to flush, then flush, then flush some more.