Apply your understanding of diffusion and osmosis to the following scenario:

You are going on a month-long vacation and have asked your neighbor to care for your tropical saltwater fish. A few days before you are to return she thought she would be helpful by cleaning the tank and refilling it with fresh water. When you get home, you find all of your fish belly-up at the surface of the water bloated and dead. Your neighbor feels terrible about it, but doesnt understand what happened. You assess the situation and kindly (though tearfully!) explain her mistake. What is your explanation.

thank you in advance for everyones help.