OK, so it is municipal water that may have chloramine in it, and at 10 ppm TDS output, the RO/DI water could easily have a lot of ammonia coming out. Even more than is coming into the DI. That is because the DI collects ammonia for a while, but when it gets depleting, other ions coming into the di that are bound more strongly (say, calcium) pop the ammonia off and you can get excess ammonia in the effluent.
Ammonia does not accumulate in an operating (not cycling) reef tank. A little added by top off is no problem, but I would replace the DI in case that is a source (or a source of worse things that can accumulate, such as copper, or a huge load of silicate).
I wouldn't be sure ammonia strips are accurate.