my tropical fish look these are having seizures

Question
I have a 27 gallon freshwater aquarium that has community fish  in it, every time I add new fish it looks like they are having seizures, then days later I find them dead. I have had the water tested, and it is fine. I've lost 5 neons, 5 grameys, and 2 sword tails. Two neons, one bata shark, and one swordfish has so far survived. Could it be too much air in the water ? It says 20 on the air pump, one air stone with extreme bubbles?

Answer
I would compare the pH of your tank with the pH of the tanks you are buying fish from.  If there is a great difference then that is probably what is killing off your fish.  The other possibility may be water temperature.  Do you float the bags in the tank and then release the fish or do you just release the fish?  dave