General Aquarium Problems

It sounds to me as if your fish are simply dying from ammonia poisoning. The species of fish you got are not generally able to survive the stress (caused by ammonia) of a cycling tank.
When you get a new tanl although the water may have been de-chlorinated and filtered etc they do not have the colonies of bacteria that convert fish waste to less harmful chemicals that you will ultimately keep within acceotable levels by regular water changes.
Fish excrete nitrogenous waste as ammonia, decomposeing matter also releases ammonia. Ammonia is very toxic to fish and will kill the fish at quite low concentrations. You need to convert this ammonia to nitrite and then into nitrate; which is far less toxic to fish and can be tolerated in much higher concentrations (regular water changer keep nitrate levels tolerable). Baceteria colonies can be built up in a tank that converts these chemicals: nitrosomonas bacteria convert ammonia to nitrite, nitrobacter bacteria converts nitrite to nitrate.
The most commonly used method of doing this is using fish species that are extremely tolerant to ammonia stress to 'cycle' the tank; mollys and danios are the species usually used. The number of fish used ultimately depends on the size of the tank. The bacteria required are probably in your tank already but some sources suggest getting a piece of filter medium, substrate or plant from a well established aquarium.
A home monitoring kit is indispensible during this process.
The process takes about a month, but up to two. Levels of ammonia in the tank rise, there should be negligible amounts of nitrirte and nitrate at this stage. Continue to make partial water changer during this period (with dechlorinated water of course). After ammonia levels peak, levels of nitrite should begin to rise, this is because the bacteria (nitrosomonas) are building up in the tank. Nitrite should than fall as nitrate levels rise as nitrobacter bacteria colonies grow. The levels of nitrate are kept within a manageable range by partial water changes.
New fish should then be added in small numbers to prevent a mini-cycle (The amount of ammonia produced is too high for the current 'population ' of bacteria to deal with, this leads to a small peak in ammonia levels until the bacteria populations catch up).
This method is becoming less popular as it puts the fish under some stress and a fish-less cycling method has been devised. This method requires the addition of ever-increasing amounts of pure ammonia until the neccesary stocks of bacteria have been established, then you simply add fish to your fully cycled aquarium. There are lots of good articles on the web explaining how to do the fish-less cycle, they do however need a supply of 100% ammonia.
Good luck

Could you post the results of the water tests?
What are the levels of ammonia
nitrite
nitrate
PH.
Do I understand that your not dechlorinating the water? It will kill the usefull bacteria that you need to be cultivating and be incredibly stressful to the fish.