I second what Mr. Ugly said - most of the Bay Area gets chloramine-treated water, and if your carbon resin is spent, you essentially get ammonia in your product water. Chloramine is a combination of chlorine and ammonia. If your carbon resins are no longer removing chloramine, your RO membrane is also being attacked by chlorine molecules and may not last long.
I've never found a reason to use any test kits other than API for ammonia. If you want to re-confirm the ammonia reading, there are a couple options:
1. Purchase or borrow an ammonia test kit from a BAR neighbor, or take a water sample to a LFS
2. Test your tap water, and a known sample (e.x., distilled water)
- If tap water is showing ammonia (from chloramines) and distilled water has no ammonia reading, your test kit is probably not off