For anyone who is following this thread...
I nabbed this picture from a post a few threads up. My alternanthera looks exactly like this with the additional pinholing. Also I am seeing the same growth tip problems in my rotala 'green' which was growing very well a few weeks ago.
This looks way too much like a Ca deficiency, not Mg deficiency. I called the water dept and the was told I could go pick up a report from last yeat but for some reason they stopped including the Ca and Mg levels. The guy told me I could call "the lab" and they could help me out. I still have to follow up on this.
I am going to start dosing Kent Turbo Calcium and skip the Mg dose. Any comments?