Sorry about the loss. Are you sure all the BG are dead. Most times that is not the case as some survive. Take a look at the link below.

http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=92486#Post92486 fish kills

http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=92438#Post92438 diseases