Chloramine breaks down to halo methanes over time so, no buildup.
And, it is usually measured in parts per billion so It would take years if it did.

However, from your description, it sounds like your water is chock full of alkaline salts.
So, your PH down is producing salts that will accumulate.

Chasing alkaline water with PH down is like playing peek-a-boo with a 2 year old, it never ends.

And not for nothin', PH readings on distilled water are meaningless because most PH meters actually read conductance.
Distilled water is an insulator, no conductance to read.

Aloha,
Weeze