feather dusters can finicky, expecially when they are newly introduced to a system, with a changing params, etc. if i remember right, they would sometimes stay inside their tubes for 1/2 a day or a whole day to clean off the nutrients / food on their crown, then should come back better then ever. also, make sure they did not eject the crown, otherwise it might be a week before you see a new one start to emerge.
as for the alk, yes the same buffer you are using for the hypo will work in this case. this situation is what they are all geared for. you can try the red sea alk, and let me know if it works for you, how long it takes to react, etc. or just go right to the kent powder, which will pop your pH up to 8.4 anyway.