and go to simulation settings first and turn off include pressure
if you got plasma in the process do !set type plsm none
and you removed 50% of the gravs
then stamp in the previus grav plant thing that you made
then go to the original city and delete all the grav particles by !set type grav none
then press F once to move one frame and there will be a bunch of fire particles. if you did it. do !set type plnt none. and !set temp all 22C. then !set life fire 0. then !set type fire grav
delete all the things except for the gravs