[HELP!]

I am on well water no chlorine

 

[HELP!]

I lost all the fish in my tank on Friday, this week, and I am devastated.  I've had my fish, for over seven years, and I know this might sound silly, but I enjoyed them so much and I would actually, play with them as they would follow my fingers.  I am on well water and about a year ago, our filter went out, and on Thursday, we finally got a new filter with an ozone attachment.  I had been treating my tank for three weeks as one of my silver dollars, was losing his tail fin and the largest silver dollar had a white spot on his nose.  I did a 3/4 tank water change, and took everything out of my tank and washed it off with just tap water.  I started adding the water back into my tank and I noticed immediately that the fish were acting unusual, at half full two of my fish starting floating sideways and at almost full two angels were dead and after a few minutes more the two silver dollars were trying to jump out of the tank, hitting the light panel with force.  I took them out of the tank and put them in a bucket with tap water, and within a few minutes they were dead also.  I have had fish tanks all my life, I am 68 years old and I have never experienced anything like this, does anyone have any ideas as to what could have happened.  This morning I noticed a white fungus looking stuff on the bottom of my tank and on my plants and rocks.  I have no clue what's going on, any help will be greatly appreciated.