Help needed confused

[tritan]

Has this ever happen to some of yous . im sure it has.Went away to school for a year and my mother was taken care of my 125gln reef tank.N o fish or corals in it.So to make long story short she topped off tank with tap water for months i asume.No lights on/tank was running all this time. So i guess im asking yous is my tank done now or do i have to start all over with new rock and sand/or can i still use them? rock still has a couple of sponges on it and glass has small flat like snails on it.Can it be saved if i do a few large water changes? getting ready to just pack it all in.HELP PLEASE WHAT SHOULD I DO?