Good news, the big cory cat is not dead (I'll just call him Lazarus from now on) - he must've been really tucked in somewhere where I couldn't see, even with a flashlight.
NH3 before water change was 0.5-1ppm, nitrite = 0, nitrates = 5ppm. After water change NH3 is 0.25ppm I think (I have a hard time differentiating btn 0.25 and 0.5ppm). The water felt a little cool this morning, thermometer said mid 70's. The light warms things up a little and that's on now.
One of the rosy barbs seems to pick on the cories - hopefully if I get another one or two it'll quell the picking - my bettas are getting picked on too, but not as much, they fight back.
thanks rbishop - I'm bouncing btn 75-80 these days, so I'm hoping the bacteria is happy as well as the fishes