Our fresh water fish are dying?!?

I recently bought the Aqua View 360 fish tank for my son. I put in tap water and treated it with Aqua Pure fish drops. I did 6 drops for 3 gallons and the water was to cold so I heated up a bit more and then added 3 drops to that. I let it sit for a few hours before adding the fish. The first fish I used where... show more I recently bought the Aqua View 360 fish tank for my son. I put in tap water and treated it with Aqua Pure fish drops. I did 6 drops for 3 gallons and the water was to cold so I heated up a bit more and then added 3 drops to that. I let it sit for a few hours before adding the fish. The first fish I used where tropical. I put in 4 of them as it was advised by the fish people at walmart. Well they died within a couple hours. The algae eater and crab lived. I dumped out the tank water and started over with spring water but did not treat it as I was told not to. I also put in a 2-5 gallon water heater as I was told that might help. I put in 4 more of the same tropical fish. They seemed fine but in the morning where all dead again and the algae eater was also dead. I took them back to walmart. They told me to try goldfish and take out the heater. I did that and put in 3 goldfish. I went into check on them this morning and they are all dead again! What is going on here? I have had fish tanks before and never had this problem. Could it be the tank? The water? The aquarium rocks? I am at a lose here. Any advice would be very appreciated.
Update: Further. I did not put any gold fish in with the tropical fish. It was a brand new tank and the first two attempts where tropical. After those failed then I tried the goldfish.
Update 2: I put in 4 of the same fish. I was told by the fish people at walmart. which i'll admit probably isn't the place to be asking. And they told me four small tropical fish of the same breed would be fine along with an algae eater in a 3 gallon. Obviously they are wrong. I took the tank back and got a new one. It is... show more I put in 4 of the same fish. I was told by the fish people at walmart. which i'll admit probably isn't the place to be asking. And they told me four small tropical fish of the same breed would be fine along with an algae eater in a 3 gallon. Obviously they are wrong. I took the tank back and got a new one. It is also a three gallon tank. I cleaned all the parts with hot water, I cleaned the rocks and the fake plants I have for it. I then added tap water and the appropriate amount of water cleaner stuff. The tank sends up bubbles through the middle tube but there is no actual filter in the tank. There is a plate in the bottom under the rocks that catches the crap but there is no filter circulating anything. Just bubbles. The tank instructions say that no filtration other than the plate is need and is meant for 5 different types of tropical fish or beta. Well anyway now that I have the new tank set up I am letting the water stand and the bubbles circulate for over a week at least before
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