Ammonia in RO/DI

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Live in the NE and have zero NH3 in the tap, rodi output and tank water.

Few things from this thread.
-even if there was ammonia in the tap, thought the purpose of the ro/di unit was to filter everything harmful out
-the comment that the membrane is damaged by chlorine, the prefilters remove 100 % of the chlorine then
-Aquasafe recommends changing filters every 6 months, if they go past their life, do they block up or start passing stuff?