I was just reading the thread about where you started this tank about 2 weeks ago. While it shows that you had filter media to "cycle" the tank, the tank is still very new as far as biofilm goes. Shrimp do much better in a tank that has been established for several months. The addition of the water from the bag may be what caused the shrimp that you already had in the tank to die, as it's qualities (ph, kh, gh, nitrates, etc.) were probably very different then what was in your tank. There is a build up of some wastes when any animal is shipped and adding that water to your tank water could have been enough swing to cause your livestock problems. Once there was some dead shrimp in the tank, the water quality would have gone down and could have caused your snail and your new shrimp to also die. As far as the worms go and the plants to have problems that quickly, I am not sure. When was your last water change before you left? Planeria, which is what the worms sound like, appear when the water in the tank is not changed enough. They are harmless to snails, shrimp, and fish. I am not sure, but the worms may have appeared because of the livestock die off causing the water quality to go down.
