thecichlidaddict said:
The mis-belief about water parameters is based on what the water is in the fishes natural environment. If research shows that a fish lives in soft or hard water, it is assumed that this is what they need.
The research I'm talking about has studied what happens in a fish when it is put in different water from it's original environment, even after a slow introduction period. It's not just saying that since a fish comes from a certain water it needs to stay in that water. As I already said, and what your experiment proved, not all fish are affected in the same way. Some fish are just not that fuzzy about water parameters and for those it doesn't matter what type of water they originally come from.
Still, others are. For example guppies that are bred in too soft water are more prone to illnesses, their spine gets bent and their offspring have a higher chance of having mutations. You can't say that they are fine in soft water then, can you? Perhaps it's their quick reproduction rate that shows the effects quicker? I'm not sure.
Another group of unsuitable fish are the ones that refuse to breed in the wrong water. Or ones that do, but their eggs either won't hatch at all, or hatch poorly. In my opinion this shows that those fish are unsuitable to live in that environment and thus shouldn't be kept in that environment at all.
Just out of curiosity, how long did your Multifasciatus live well?
I myself started out without measuring any parameters. I recently "started my hobby again", better prepared this time. It turned out that the water in my soft water fish tank was harder than it should be. There are a few really tough fish in there, ages 7-10 years. Still, these fish have not reached their full size nor have they ever bred.
Another thing I'm ashamed to say is that these "oldies" are only a few of many fish I have kept. Most soft-water fish I have kept in that quite hard water have died too soon, only after 2-3 years. It's hard to say whether or not just the water parameters are to blame, but I certainly don't rule that out. Once I get the outside canister filter for that tank, I'll start filtrating through peat to lower the hardness. After that we can see whether or not the majority starts living to their expected age and size.