Well, considering you've admitted that if you leave a tank alone and it gets "Old tank syndrome", or as you put it, the fish "adapt" (quite similar to "get used", I find...) to the water and are fine. But new fish that have HAD to change water sources (and probably have been in clean water) die from the neglected parameters. I prefer to have fish I buy live, so thus, I keep clean water. Works for me, usually when I neglect any of my tanks fish start dropping.
There have been many threads like this in the past. Hence Niko's (among others)
opcorn: spam. I really don't think there's much to be gained from this thread, as what people find succesful is what they'll do, for the most part. I'm happy changing water. I think bright colours, more activity and breeding signals health (because, naturally, sick fish would be less likely to breed). I'd rather not get neck-deep in this thread though.
There have been many threads like this in the past. Hence Niko's (among others)
