sudden loss of 2 fish

Question
Hello, I just started with my first aquarium 2 weeks ago and everything seemed to be fine. Today I woke up and found 2 fish had died. I tested the water and the results were GH 120, KH 80, PH 7.2, NO2 0.5, NO3 0.0. The tank is a freshwater 6gal. wall tank. I had 2 danios, 2 tetras, 2 female bettas, and a snail.  I lost 1 danio and 1 tetra. The bettas have been hanging out in a corner above the filter and in talking to people I was told to move them to their own separate tank. Now some of the other fish are hanging out in the corner as well. I have turned off the bubble wall. The only thing I did different yesterday, was that I gave them frozen blood worms for the first time. Please help.
Thanks.  

Answer
Hi,
Firstly, it is good that you are testing your water, but unless you know what the results mean it is useless. Your GH measures the hardness of the water (General Hardness). Basically, 0 to 70 is very soft, 70 to 140 is soft, 140 to 210 is medium hard, 210 to 320 is fairly hard, and 320 to 530 is hard. Some water is harder but only for some specific species of fish. Your water is soft, which is good for Tetras. NO2 is more frequently called nitrite, and is basically poison, so any levels over 0.0 is dangerous. In a new uncycled tank that is common, so just do daily 30 percent water changes until it is 0.0. NO3, ammonia, is also poisonous, so it is good that is 0.0. The "neutral" pH is 7.0, but anything between 6.5 and 7.5 is ok for most fish.
Danios need plenty space, so I recommend taking the existing one back to the fish shop, and buying more Tetras, so you have 6. Male Bettas are VERY territorial and aggressive, but the females are not, so you can keep them unless they become aggressive towards the other fish.
6 Gallons is very small, so you should not add any more fish.
You will have:
6 Tetras
2 female Bettas
Your snail

I hope this has helped.
Good luck,
Kathryn