I started my tanks on tap water..."Well" water actually...(non-Federaly regulated)
I didn't kill any fish...
I had macros in the display until I built and moved them to the fuge...
I never had problems with nitrAtes or phosphates, but I was experiencing a continuous unattractive "diatom growth pattern"...Which after testing, revealed an excess of Silicates in my source water...
I then "sponged" out the Silicates and switched to RO/DI water so I wouldn't continue to add them and the diatoms cleared up and I believe my tank looks cleaner and healthier (both subjective observations)
My tap water didn't cause me any "setbacks", but I do believe it was keeping me from "progressing" to (my tank,my choice) my goals of a clean, clear, thriving reef.
However, a few years ago, my mother ended up in the hospital from an outbreak of cryptosporidium(sp) from her 'Federally Standardized" citified tap water...:nope: