I think you should wait as least 6 weeks before putting any livestock. You should check out other postings in this Forum which should be very helpful...
IMHO, I don't think you should put any livestock when you are cycling. It is normal for your water to be cloudy and toxic within the next 1 - 3 weeks and anything you put in will die.
I searched many forums but not many people really give definite answers. Actually I also see those expensive paired ones fighting... I think it's their character to be dominant.
I also put my newly purchased fish into my main tank immediately but I still do acclimation first. Sometimes I notice some white spots so I put in Para Guard and it works for me...
Don't give... It's normal. Just try again.
I also had the same experience so I bought Para Guard by Seachem and added it into my main tank whenever I have new additions and it was fine after that.
Go to a hardware shop specializing in pipes and sanitary wares. They have a better selection than buying these from lfs. Otherwise you can try Madpetz- they have some.