inherited a tank, fishless cycling now

You might have added too much ammonia. More than your aquarium can handle in 24 hours. Even a fully cycled aquarium has its limit. Try not to add more than 5~6ppm every 24 hours. If you see there is still ammonia at the end of 24 hours, you should either decrease the amount of new ammonia you add to the aquarium, or skip one day of ammonia all together.

As you have seen your PH dropping, you should do a partial water change to restore the water buffer. The good bacteria do not do well in acidic water when the PH is too low.