What the heck are these on my glass?

[ReefGrrl]

First thing I do every morning is look at my 29g cube tank to see how things are (and sometimes Plectranthias Inermis is still out front hunting, before heading back into the rocks to hide for the day, so I get to see him).

Anyway, this morning I found these flat white blobs all over the upper left front and side walls. After I stopped freaking, I spent about 2 hours on the web looking at pictures but couldn't turn up anything that matches. One of my turbo snails and one fighting conch were in the area. I have seen one or two of these blobs scattered here and there before, and took them off with my mag float when I cleaned the glass.

The cross-section of these things is hard to see, but looks like it's very flat, with a slight raised area in about the middle. I estimate there are about 100 of them and they don't seem to be moving. I've used a sharpie to mark the locations of a couple of them, so I'll see if they move slowly or not at all.

The closeup shows the shape, which is what I haven't been able to match in any of the pictures I've seen. I've combed through online ID guides, nothing there either.

Tested last night, and calcium was 420, mag was 1210, alk was 11.3 (story here: I started dosing with polyplabs One, four days ago after testing params and having them in balance - now alk is out of whack, going to rebalance gradually over the coming week).

Thoughts? Advice? Should I be getting a giant tote of saltwater ready to rescue everything?