Sorry for your ram.
They are a very delicate fish IMO and won't tolerate any swings or spikes with an uncycled tank...
The Prime converts....
Clearly printed in link you provided that I have read before....
I use seachem SAFE instead of prime due to my large volume of tanks(1,000g++) and the fact it is WAY cheaper....
You can use prime every two days for converting but I really expect your tank/filter to come around shortly.
Often GBR purchased from LFS(besides MINE) are genetically inferior and already stressed and weak.
Good luck you are getting closer to the fun part...