ok so i read through it and....yeah. first question. how old are they from the time they popped out of the rockwool?
if it's the first time you're using the hydroton, you don't need to wash it. it's already sterile
out of wack ph won't burn the tips like that. it'll burn the leaves evenly. JohnnyPotSeed is right about ph locking out nutes but in plants so young, well wouldn't be a problem since they can live on fresh water.
here's the thing. damage won't always reverse itself. so keep growing if the new grow comes in clear then your plants will be fine. If the damage spreads, replace all the res water with fresh water (no nutes).
from your pictures it looks like the new growth is coming in clear. I'd say your best course of action right now would be sit and wait. people usually screw up when they try to do too much.
