I have read of fishkeepers with ~0.25ppm ammonia right from the tap from their municipal water supply. Mainly when they use chloramine as opposed to chlorine. All you can do is dose heavier than normal with a quality dechlor like Seachem Prime or Safe. It should get converted over to nitrates in a few hours. Problem is, now you're starting with some nitrates immediately after a water change. I wouldn't sweat it as long as you can keep nitrates reasonable between your weekly water changes.
