OK, here's the latest update.
I went to the store and had them test unconditioned tap water again, first for ammonia and again I'm not sure they left the strip in the water long enough. It read 0.5 immediately after pulling the strip out of the water. Then he used a multi-test strip and said things looked fine. The water was slightly hard, but nothing serious.
After he said that, I compared the ammonia strip to the chart again (a minute at most had passed) and it was reading 6.0! When I pointed this out, he said that the ammonia test strips will continue to darken in the air. Is this true or does the tap water really have 6.0 ppm?
When I got home, I added 4 more drops of Prime to each bowl (they were in Maracyn II recovering). The next day it was like a complete 180! They were both extremely active and alert compared to their usual lethargic state from the previous weeks/months.
I continued the Maracyn II treatment for the full 5 days and looked them both over to make sure the redness of the fin tips was gone.
I took them out of the Maracyn and used 8 drops of Prime to condition the tap water and they both did very well for about 10-12 days, but right after the most recent water change two days ago, I noticed them becoming lethargic again and I know I added Prime. Today the fins had bright red tips again. I'm not quite sure what to do now.