I've had really good results in QT whenever I've let the QT completely cycle which is around 30 days or so. Seems like every time I hurry, there are problems.
But sometimes you have to set up a hospital tank quickly and adding ceramic materials, foam filter pads, etc. that have been soaking in the DT sump for at least a month, can work really well.
Recommend Seachem Stability or Bio Spira to help cycle along. Seachem Stability is a bit slower but has a better ability to adjust and maintain ammonia levels. Soaking HOB foam pads with either of these really helps. Also use a foam bubble filter with the foam "soaked" either in the sump or with SS or Bio Spira.