nah it wouldnt kill the potency.. the only damage it could possibly do is losing some yield if your pH is too low.. But this would make a difference in quantity, not quality...I would wash with higher than 8,5, btw, I would wash with more like 10, to make sure no DMT dissolves in the water...
The only possible thing is, if you smoke a more oily impure dmt, the impurities can 'protect' the dmt from heat of the lighter, for example, an you vaporize it more effectively thus having a stronger trip.. But then if you have pure stuff, all you have to do is be careful not to put the heat too directly
What is your friend's smoking method? maybe he's burning the spice with too strong heat or doing something else wrong.. Is he holding the smoke for long enough, taking big enough hits ?