I’ve read the api ammonia test kit regularly gives people a false reading of .25, that’s why I was wondering on the test kit and ammonia reading. Had to be something pretty drastic in such a large volume of water to affect things so quickly. Safe to say something in the water is really causing a detrimental effect to the corals. I would keep doing large water changes matching the params of the new water as close as possible to the tank water, especially alk and temp.
ok thank you