Almost all aquarium books that I have read state that octopuses demand optimal water quality and that they can not endure any water pollution (Haywood, etc). Most of us immediately associate the words 'optimal water quality' with the words like 'wet/dry', 'protein skimmer', 'ozone', and 'considerable financial undertaking.' In stark contrast, Dr. Hanlon has published some surprisingly forgiving water quality parameters. For example he states that at least for the five species that he dealt with, no reduction growth or feeding was noted at pH's as low as 7.5, salinities in the range of 32-38 ppt, and both ammonia and nitrite in concentrations of 0.2 ppm on a long term basis. Similarly, he reports that nitrate concentrations up to 500 ppm did not seem to affect growth or feeding much, if any. However, he mentioned that nitrate concentrations above 100 ppm may affect reproduction. One water quality fact that is crystal clear, is that excessive heavy metals, especially copper, are deadly.
I'd say that soft corals are much hardier than octopuses, especially the leathers and the like.
Anecdotal evidence doesnt do it for me and still isn't an excuse for nitrates as high as 500ppm, pH as low as 7.5 or low salinity levels. Not yelling just pointing out that years of experience here strongly dissagree.