was the peat you mixed in unprocessed stuff or was it ph-adjusted? the raw, cheap stuff is akin to buying bick coco.. you have to process it and make it a proper pH or it will lower pH significantly.
is it possible too hot? looks more than xplant shock.
is there enough drainage.? the withering seems to be more than something simple like this, but mentioning for shits and grins.
Try a soil slurry or pH of runoff... if it's crazy low it should be obvious. the volume of water you use will dastically impact what you see. so, try to be consistent about it to make it more useful in future as you have an idea of how it is skewed in a soil slurry or even using runoff water. at some point try to get a baseline wwhn things aare runnign as smoothly as possible. it's all relative from there.
if you don't disturb the rootball much, it shouldn't get shocked. in 3 years, so far i don't believe in xplant shock... (like wild e coyote ignoing gravity, "hahah" not being serious -- but now something catastrophic will happen to me in this regard for typing out such hubris, like some sort of greek tragedy.) i think this is possibly more than just xplant shock. something is out of balance in substrate or feed?