It's late, but I just have to tell you that it is definitely not your fault! Don't even think of blaming yourself for this, and please listen to me because I have beat myself up over almost the same issue. Seriously, I have water issues as well and I have mentally tormented myself to the point where I almost gave up the entire hobby because of all the problems that I encountered. For example, yesterday I had to boil an entire 5 gallons of water using a little kettle because for the past month there has been some sort of bacteria in my water that kills my male's fins. Ever time I'd do a water change they'd get rips and holes in their beautiful fins for no reason. I finally pinpointed it to my water and now I need to convince my parents to shock our well. It doesn't affect other fish or my females. I'm guessing the same thing is happening with your water with a worse effect. This does NOT make you a bad owner, in fact it just proves to me that you are a good person because of your reaction. An uncaring person would say "meh, it's just a fish" and move on, but a good person always takes things out on themselves because they actually care and are responsible. I KNOW FOR SURE that you take great care of your fish, and I'm not the most trusting person in the world, so what you need to do is remember that you are a great owner despite having problems that are out of your control. This post really hit home for me and I hope that what I have said will help you to NEVER blame yourself for this. This kind of thing can and does happen to many people, we just don't hear about it because it happens behind the scenes of the forums.
On a proactive note, I have considered spending the money to buy a UV sterilizer and a RO unit and hooking it all up to a holding tank so that I can start fresh with my water. This may be an option for you as well. I find my water has "good" periods when everything is just dandy, and "bad" periods as I described above and this is why I haven't spent the money on this setup yet, but I think that it is definitely time for me. If you don't want to be buying bottled water each week a similar setup should remove everything from your water, then you can just add a blend of essential minerals and be all set.
I wish you the best of luck and I hope that my suggestions may be of some help. Feel free to PM me any time to chat or just vent
. Maybe we can work something out together. ~Kim