If your ph is 6, then thats the reason for your tank stall. If you havent done a water change yet, its time for a big one to restore your buffers. Then add @2ppm of ammonia & lets see how things look in 24hrs. Make sure you keep a close eye on your ph (daily) because as your tank revs up processing everything, your ph may drop again.
+1
Yup, time for a large water change to boost the buffers and such. Keep testing the pH and do a large water change if it dips back into the low sixes. If you have to do more than one PWC to get the pH up then so be it, it won't hurt anything just give it a half hour between water change and test so everything gets mixed well.