I've seen the first reference but unfortunately it's speculative, too. WetmanNY's site is great, too, but the articles there aren't immune to speculation and bias themselves. I admire erring on the side of caution with all substances added to the tank's water, but just like anything it can be taken to too great an extreme--particularly when it's not backed up by very much experience. I, personally, have never been able to observe any signs of irritation in my fish through the use of Prime, Stress Coat, Stress Zyme (yes, once upon a time I used this ineffective product), Tropica Master Grow, Flourish Iron, Flourish Excel, Flourish Potassium, Flourish, or MelaFix. I definitely have observed aberrant behavior following the use of Kent Pro Clear, Seachem Acid Buffer and Alkaline Buffer, and Seachem Discus Buffer and Neutral Regulator, all of which can be dangerous is used improperly and sometimes even when they are used properly. I've even seen fish quickly learn to avoid chomping on solid granules of potassium nitrate, potassium sulfate, and potassium chloride, but the effects have been limited to spitting out the chemical and swimming away. Water conditioners IME have been the most benign of additives I've used.