Very active starter suddenly isn't rising

I started a new starter six days ago.  Twenty-four hours later it was bubbly and had doubled in height.  On day three it had oozed out of its jar.  So I moved it to a larger jar.  I started feeding it every 12 hours as instructed.  It rose by about 50% the first feeding, and after that it just stopped rising, though it continues to bubble. I'm on day six now.  It continues to be super bubbly but isn't rising. I stopped feeding it every 12 hours and went back to a 24-hour cycle, which has made it bubblier but not likely to rise.  

I split it and tried adding whole wheat flour (50%) to one half.  That one stopped bubbling at all and got tossed.  The half that got unbleached all-purpose is still going.

A few additional notes that may help in diagnosing the problem:  I had been using tap water I left out for 24 hours to dechlorinate.  On day 3 I accidentally used straight tap water.  After that I started using tap water I'd boiled to de-chlorinate.  I'm in New Orleans, so it was over 80 degrees outside (and consequently a good 80 degrees in my kitchen) on days 1 and 2.  On day 3 it cooled off a bit.  It's been hovering around 80 indoors for the last few days.  The thermometer in my kitchen insists it's been at least 75 degrees, and often warmer, throughout.  It's also been reasonably humid.  For reference, it's currently 75 F (25C), 91% humidity.  My kitchen thermometer reads 81 degrees.  

Photo:  current state, 12 hours post-feeding.  It's bubbly, but it hasn't risen and weirdly it's developed a dusty top, like someone sprinkled flour overtop.

I'm going to feed half right now to see what happens and leave the rest till tomorrow.  My kitchen is a regular science lab these days.  But I'd love advice from those who have done this before!