Green Barbs going belly up?

Question

We recently just got 2 green barbs to go with the 2 tiger barbs. Everything was alright at first, but then one of the greens started to hang out around the top of the tank. Knowing that this was not a good sign. I scooped it out and put it into some clean water. It died shortly after. The other green was fine, until today when we replaced the dead one. A few hours after we added in the new one, it also bellied up and died (did the whole hang out at the top, can't keep itself upright thing). The other green barb started to belly up as well, but seems to be doing somewhat better. It's still very very weak, but it's not floating at the surface any longer and looks like it has some str back.
What keeps going wrong?
All of the fish are in a quarantine tank that I do daily 50% water changes in (tank isn't cycled) to keep the ammonia down.
The regular tiger barbs are absolutely fine... but these green ones just keep dying on us.

I think the other barb is going to die soon now. Just went to check on it and it's back up at the top again.
I just added some Amquel to the water to see if that will help any if the ammonia is the thing that's screwing the fish up.. *SIGH* Poor fishies.

Answer 1

Well, to keep the answer simple, as it seems you understand cycling, I would say that it's either the green barbs were not healthy to start with, or that they didn't do well in the uncycled quarantine tank. So, try another pet store and cycle your quarantine tank. I can't help but think one or the other would fix the problem.

Answer 2

Are the fish from petco?.....It sounds like the fish are going into shock. Your water levels could be way different from the store, for example your ph could be higher or lower. When the fish go through a sudden change like that, they can be suffocated. That probably explains why the fish were at the top of the tank, because that's where the biggest oxygen supply is. Over time your tiger barbs have grown accustomed to the living conditions. Make sure you do water changes regularly and always try to use ro/di water. Tap water is never good. Also, when you get your fish, make sure you float the bag on the surface of the water for at least 30 minutes if not an hour. Trust me, there is plenty of oxygen in those bags to last a while. How do you think they ship them? Anyways, this will even out the temperature of the bag. Then poke one hole in the bag and let it float for an additional 30 minutes. This will let the fish get slowly acclimated to the water conditions and will help the fish from going into shock.