I have a 1 week old 150g tank and all levels test to be fine. Here are the facts:
PH:8.0
Temp:81
Nitrite: 0.0
Nitrate: 0.0
Ammonia: .025ppm
Filters: AMiracle Wet/Dry Filter with bio balls 500g/hr & Eheim Pro 3 2078
Substrate: Crushed Coral Aragonite
Decorations: 200 lbs of Natural Red Stone

Tank is crystal clear. Upon the first day of set-up I have added the recommended amount of Cichlid Salt/Minerals. I also added stress coat and also the recommened amount of natural bio/bacteria. Bought the fish today, thinking the tank had completely cycled. After introducing fish to aquaium (1hr, by slowly adding my water to a bucket of the water they came in) I added the fish to the tank and they all died within one hour!!???

Well luckly for you, you should be able to return all them since it happened so quick, but with regards to your cycle did you do a fishless cycle or did you have fish in there while cycling it, because a tank won't cycle if there isn't anything to break down. Also, (i don't know about where you live) but where i live some pet places feed their fish literally once a week so the water stays clean, and keep the temperatures at like 70 degres fairenheit, to save on electricity, but that harms the fish, so make sure you buy them when they are healthy. And if you go to start again (i don't know how many you put in) don't put too many in at once because the bio-load won't be able to handle it, but i don't think it was from ammonia or nitrite, the only thing i can think of beside the fish being sick when you got them would be not enough oxygen in the water because that can kill fish quickly.

There are many different ways, and everyone has their own opinion, many people will say air bubblers, but others will say it is a waste of money, you could ge a powerhead, basically anything that keeps the top water moving, i would suggest an air bubbler, because they aren't all that expensive, and i personally like the look of the bubbles, but its up to you. By the way did you get your money back for the fish?

i bet that your problem is low oxygen. when i was rearranging my tank i accidently in hooked my air house to power head and i left for alittle bit and i come back and all my fish are at the top of my tank gasping for air so i hooked it back up and within 15 minutes they were all swimming around again. I also have a eheim pro 3 filter put mines the 3e. i willing to bet thats your problem. buy something to put air in your tank. im willing to bet theyll live next time

I have no problem getting a power head or some air stones,,,,but I keep getting told that the wet/dry filter produces plenty of oxygen....is this not the case?

@dandman18 and thanks to pro68camaro too...
As soon as I place the fish in the tank they are swimming and having good movement but moving their mouth and gills very rapidly.....after around 40 minutes they all start to move their bowels and then they become very fatigued and stop swimming and then croak...........all in around 60-90 minutes.