Every time I've done it i tested for ammonia, nitrite, nitrate, and phosphate. The only test that came back in high numbers was phosphate, but since I was only keeping triggers and such i was never really concerned as my tap water also tested just as high. I agree with your last line, I would not recommend it at all. I am very pleased, now that I am older that i never had any fish suffer. When I first discussed it with a saltwater LFS owner we were discussing that extreme fluctuations in ph is something that bacteria really hate. Well that got us talking about if we were to keep the ph and temp at the same level, would there be bacteria that were able to survive both fresh and saline conditions? I gave it a shot because I was young and dumber than I am now. What I always did was severely cut the bio load if I went from fresh to salt. I remember one time i had an African mbuna tank for around 2 years and one day decided to change that same day I only brought home 1 four inch Picasso trigger. Now I know that doing that can also cause a crash, but I was assuming that there was a kill off of some bacteria from the change in water salinity, and that the remaining bacteria were too low to support much marine life. From there I slowly added life to the tanks and i never had any real kill offs other than a pink block anthias which i was too much of a saltwater noob and that thing never ate. So I guess my point is, there is something to this, and it can be very successful. however I do not want anyone to go out and try it and end up killing innocent fish if it were to fail. I did a lot of stupid things in my early years of saltwater fish keeping, but I don't believe in dumb luck. Firstly I have never had any luck but bad!!!!! Secondly it worked multiple times for me. Including brackish I would say i have done it without a blip at least a dozen times. I have not done it in a while because I fell into a niche that makes me happy in fish keeping, when I was younger I wanted every fish I saw. I just think we are doing an injustice to fish keeping if we always just accept things the way that they are, the hobby will never grow. No one person knows everything about a given topic and I am not trying to say you are making that claim, but where are we if we never try to understand why somethings happen that go against what we think we already know??????