My tank is new, had been up and running empty except for 1 live plant for a week, I had Petsmart test the water before buying my fish. I added 3 Ryukin goldfish and 2 algae eaters yesterday at about 1:30 and by 11 pm 2 of the goldfish had died. The 3rd is swimming about and the algae eaters seem fine also. I have the proper air pumps and I just can't understand why they would die so fast? They were not picking on each other either... after I let them float in the tank for 15-20 min, I released them and they seemed fine for about 2 hours then I saw that one was at the top of the tank a lot with his tail pointing to the bottom... the other one seemed to hide in the cave a lot... the 2 fish that died came out of the same tank... could they have been sick already? I'm wondering if they may have had swim bladder and if so could that kill them that fast? I noticed about 8 pm that they were sitting near the bottom of the tank and one was in the cave, I thought maybe they were just resting... I had to go out and when I came back a couple hours later I found both of them were dead but the 3rd fish was fine swimming about as were the algae fish... so strange!

Any help would be greatly appreciated, I am new to the aquarium scene, I haven't had one for about 25-30 years (when I was a kid) and want to learn quickly so as not to harm any future fish.

Petsmart, like all chains use one filter system for the whole store. So, if there is something going on in their tanks, it spreads to all of them. I found, my petsmart gets deliveries on Wednesdays. So, I get in there quick and pick out fish fast and get them home.
If you look at all their tanks and see any ill looking fish, DO NOT BUY any fish. Yes they have a 14 day warranty, so what. I got tired of killing fish.

You did not mention the size of your tank or filter, very important. Test your own water, also add bacteria. When you have a new set up start with 1 or 2 fish. It gives your biological filtration a chance to grow in order to handle the fish waste. My guess is too much fish waste for the filter to handle and or water temp. and PH could have been off. The most harm comes from temperature swings.

Thank you for the info, appreciate it. I took the dead fish back to them and they did exchange for me, I made a point to look at how active the various goldfish were and decided to stay away from the Ryukin for now... I brought home a black moor and two teledioscope (sp?)and these fish are incredibly more active than the original... sadly by the time I got home the last surving one had died also. The store rep explained to me to always ask when they get their stock in (it was Friday) and possibly wait a day or two to let them settle down... she thinks maybe the stress of their delivery then being rehomed again within 24 hours may have been the problem.

I have a 20g tank that I started a week ago using the proper conditioners and chlorine removers... I added the good bacteria to help build an eco system and the water is a steady 68' so I'm not really sure what happened to them other than maybe just the shock of adjusting... they were babies also, maybe not as hearty as the bigger fish. Hopefully this new group of fish will do much better, so far they are swimming around like crazy exploring, much more active than the group from yesterday! I feel so bad with the original 3 dying, its very disheartening when I'm trying to start a hobby that I once enjoyed tremendously as a kid.

The help at these stores are usually "kids", take their advise with a grain of salt. The fish have a better chance of survival if you remove them from their tanks. That is my opinion only, however I'm in the hobby for 50+ years.
Yes, the fish are under stress when delivered. Let them calm down in a clean and constant environment at home. Like I said, The stores run with one filter for all the tanks. So, any disease or contamination spreads to all their tanks real fast.

PS. 20 Gallons is not that large for 2 adult goldfish. Remember gold fish produce more waste then a same sized tropical due to their body mass.