1. Dichlor dissolved very quickly; just dump it in your deep end and keep people out for 15 minutes or so. (If they get in sooner, and swim through the 'hot spot', it won't hurt them but might sting their eyes and bleach their swimsuit.)

2. If the roughness is ON the plaster, you can do something about it. If it's IN the plaster -- that is, if the plaster itself is pitted and rough -- fixing requires major repairs.