My Vallisnerias (corkscew and jungle) seem to be dying this am. New growth is turning transparent and a much lighter color of green or transparent.

They have been grown well and the only changes I have made are:
Six (6) days ago added 10ml of Excel which is label's dose and nothing after that.
Yesterday I increased Plantex dose from 0.52ppm to 0.86ppm.
My PH changed (bubble rate inadvertently slowed down) from 6.6 to 7.0 and have gradually changed it back to 6.4 with CO2, of course.

Feed back please.