Join Date: Jul 2010
Location: Outside Philadelphia, PA
Tap water can vary a lot through the seasons, going from very good to very bad. Also, you do need to match the new water to the temp of your tank, or at least be very close.
A 50% water change at a temp of 60 is a lot different than a 50% water change at a temp of 85. In winter, I can get tap water as cold as 45.
About all you can do now is add the prime, which you have done, and wait this out and hope. Let things come back to normal and consider this a lesson learned.