Originally Posted by Caliban
The profile says under 7.0 pH with soft water, but this is the same thing I've been running into. Literature/Info Pages say one thing, but fish owners seem to be saying they can live in higher pH. I probably won't go with them. I tend to try to cover all my bases, so why risk it if I have other options. Plus, my boyfriend is starting a tank and wants neon tetras, and his town has a different water supply than mine :D.
I understand the issue with varying opinions. Bear in mind, the water parameter section is headed "Ideal" which means that the particular fish may do fine outside these parameters, but will be best (= healthiest and less prone to disease issues) within the parameters. "Optimum" is another word sometimes used for "ideal," and in the plant profiles I use this a lot. In those profiles I have written, I will insert issues around water parameters when such are applicable [more on this momentarily].
All characins, with very few exceptions, occur in very soft and slightly acidic water in nature. Those species that are now being commercially raised in tanks have frequently been raised in harder and basic water; Neon tetra are such fish. While it is no doubt true that after several generations they seem to manage better in such water than wild caught fish would, there are still many fish species that don't totally "buy into" it. Glowlight Tetra for instance will not be as colourful in hard basic water as they will in very soft acidic water, in spite of having now been raised for decades in tanks. There are species that will never spawn in hard basic water. Sometimes a shorter lifespan is all that we can detect from this. What all of this says to me, is that while the fish may adapt to some extent, it is still having some degree of difficulty. Unfortunately we can't ask the fish themselves if they mind, or to what extent they mind.
But we must all remember that these fish have been programmed by natural selection to live in a specific water for more than thousands and even millions of years, and changes are bound to have some effect.
Back to the profiles; I wanted to mention that the information contained therein has been researched extensively using several leading ichthyologists and experts in the particular fish species. When I write a profile, I use data on which these scientists and hobbyists agree, and if there is significant difference of opinion from such experts, I mention it. So you can take it that the profiles are scientifically sound. That is not to say there cannot be disagreement from knowledgeable aquarists, nor that such disagreement is itself wrong. In this as in so many areas of life, there are many variants, and many or all of them may work; but there is also the trusted obvious that is less risk, i.e. the "ideal" or "optimum" for the good of the fish or plant.