If your water supplier uses chloramine to disinfect the drinking water, a slight reading for ammonia is quite normal. Chloramine is a compound usually composed of or 4 parts chlorine, to 1 part ammonia.
The most important thing to remember is not to toss the bio filter material.
If the pads are gunked up, it is best to just swish them around, or squeeze them out in water change water until less gunky.
I only throw away that type material when it is in tatters, and then keep one running when changing out an old one, until it is fully seasoned.
If this goes against your grain, get another HOBack filter and put only small pieces of lava rock in it, in a mess bag that will be a constant no change biofiltration unit.
Just occasionally shake it out in water change water, and quickly return it to the filter.