So, let me get this straight...your RO/DI water has 7+ ppm of ammonia in it? That doesn't make sense.
As for your source/tap water, Prime will detoxify ammonia up to 1ppm. You may have to start doing two smaller water changes (25-30%) during the week, so your biofilter can handle the amount of ammonia you are putting in the tank during water changes.
I would find the water quality report for your water supply, usully from the city. That level of ammonia in your tap doesn't seem good. If your water sample is higher then the average ammonia in your water or even higher then allowed i would call you water department and find out what actions need to happen.