Okay, well unfortunatly you didn't really cycle the tank. Cycling means building up a source of nitrfying bacteria. The first group eats ammonia and produces nitrites, then bacteria form which eat nitrite and produce nitrates. In freshwater aquariums the way to get rid of nitrate buildup is with weekly water changes.
The established filter material you used would have that bacteria on it but if you don't feed that bacteria (a source of ammonia like rotting foood, detritus, or pure ammonia) then the bacteria slowly dies off. Cycle is a product which contains some types of bacteria that eat nitogen products but without a food source they too will die off.
Thus you have no nitrates as your tank hasn't esatblished the right kinds of bacteria yet. So you are going ot be doign a fishy cycle now. The plants will help but keep an eye on ammonia and nitrite levels. Keep the ammonia under 1ppm and the nitrite under 0.25ppm. Don't add any new fish yet, let the bacteria grow and accept the level of fish you have now. You may need to do daily water changes as certain points to keep the levels of poisons low and use a dechlorinator if needed.
The angel may have been in shock if not acclimated well enough (ie there was a major change between the fish store water and your water). Next time empty your new fish into a clean bucket (use only for fish) with the bag water. Slowly start to add fishtank water until you double the amount (20-30 minutes or so). Then remove half of the water and redo. That should help your fish adjust to temp, pH, hardness etc...
That angel may have been weak and not able to withstand the changes you put it through whereas the other fish may have been hardier.
good luck and keep asking questions.
