having the temp at 28 will speed up the illness and do nothing but make it go faster. a study was done and at the temp of 32 the parasite dies completely, and at 30 stops reproducing (which is good) so bump your temp to 30 (depends on what other fish you have in there as well)
i got my whole tank consumed the one time, but i treated it heavily with methylene blue and salt (not heavily on that though) then kept the meds in there for a week after there are no signs of the illness. then did a water change, cleaning the gravel very well because the parasite will rest there before looking for another host. then added carbon to remove any left over ick and boom was all done.