Its cool. I know you're stressin' but take a breath and get your zen face on ^_^ We know if you didn't care you wouldn't be here. I apologize if I sound short at times. I dont always have alot of time when i answer these things (i work, run a house, raise a kid, run a fish room and blah blah blah) so I'm sorry I if I just throw facts at you without more in-depth explinations.
Nothing is more intimately linked than a fish and the water it lives in. They breathe it, drink it, move through it, sence through it, and they absorb hormones and chemical cues from other fish in it. The quality of the water effects them all the way down to a cellular level. pretty much all of their life processes and behavior are governed by chemistry and conditions of the water.
You want to keep ammonia at 0, nitrite at 0, and nitrates under 20ppm? (Some one remind me! All my crap is on an AWC system so my last reading is rarely above a 5 on a bad day) ideal ph readings depend on the species.