450 is not bad, yes on the high side but that is the max I would go.
Yes, I would stop adding a "that stuff" and would not even bother with iodine.
dKh is related to Alk. dKH should be from 7 to 11 and Alk should be 2.5 to 4.
And as noted before me, they are all integral to eachother.
Ph can...