Originally Posted by RandallW20
I figured as much. So in other words, it would be in this persons best interest to invest in an R.O. system regardless just to be on the safe side.
Not to mention that the RO water would be better for the fish anyways even if the well water was ok.
No to the last sentence. RO water on its own is in fact unsuitable for fish because it is so pure. Such water, like distilled water as well, does not generally exist in nature and cannot support fish or plant life.
All natural water that supports fish or plant life contains substances that benefit (and are essential to)that life. Water that passes over rock generally contains minerals, primarily calcium and magnesium, but also iron, zinc and maybe others. The amount of mineral in the water determines the hardness. Water that passes through heavy forest or contains considerable organic matter (leaves, wood, peat) will be rich in nutrients and usually soft with respect to mineralization unless it also passes over rocks.
Most of the fish we maintain prefer one or the other, and except in extreme cases some adaptation is possible so many of them can live healthily somewhere in between. Very soft water (with little or no mineral content) can have as detrimental an effect on aquarium fish as very hard water. And, all fish need some mineral to be healthy; some is contained in fish foods we feed them, but some they obtain from osmosis when they absorb water into their cells. This latter point is why the water parameters are so important; the fish must absorb this water, and its bodily functions have to react accordingly. For instance, the fish must regulate the pH of its blood to equal the pH of the water it lives in and absorbs, and fluctuating or adverse pH means the fish is working harder to adjust, and this causes additional stress which leads to health problems.
The first thing is to determine the hardness and pH of the well water, and what it contains. It is very possible that it may be perfect for an aquarium, although the iron issue would concern me; too much and I agree a RO unit would help. But the RO water needs to be mixed with some untreated water to restore a bit of the necessary mineral content.