06-17-2011, 04:10 PM
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The passage cited in post #4 is correct, but one sentence in that could be misunderstood, so allow me to explain. The sentence is,
| Most freshwater fish live within a pH range of 5.5 to 7.5 (African cichlids can go up to 8.4). |
This does not mean that all fish can manage within the range given, far from it. What it does mean is that all aquarium fish fall somewhere within this range.
Many commonly-available fish are tank-raised and adapt more or less to a slightly wider range than they would have in the wild. But there are still some specifics. Livebearers require medium hard to hard water (which has a corresponding higher pH, anywhere from 7 to 9 depending upon the hardness and which minerals cause it), rift lake cichlids the same and better at the higher end of hardness and pH. Soft water fish do best in soft to medium hard water with a correspondingly lower pH, somewhere between 6 to 7.6 depending upon species. Wild caught soft water fish will not do well unless the water is soft with a lower pH though this can vary a bit since it is the hardness that is actually critical.
Many soft water fish do not last as long as their respective lifespan when kept in hard water. Calcium blocks the kidneys for one thing, and there are other similar issues. This is not detectable externally, the fish may "appear" fine, but suddenly it dies after say 3-4 years instead of the normal 10 years. This particular example is the cardinal tetra. The species will externally look the same in soft water or hard water, but internally trouble is there and the fish up and dies sooner than it should.
Selecting the substrate is important for the buffering aspect you mention. Substrates for a tank of soft to medium hard water fish should not contain calcareous substances (limestone, dolomite, marble, tufa, coral) as these will raise the hardness further, and corresponding the pH. This type of substrate is ideal for rift lake cichlids, and livebearers, along with those other species that are best in such an environment naturally. An inert substrate material will not affect water chemistry of itself, though what naturally occurs in the substrate will. But that is another topic.
The pH is important because fish must adjust their internal (blood) pH to match their surrounding water. This is one reason why pH fluctuations are so dangerous, if they are significant. A minor fluctuation of less than 1 d pH over a period of time is tolerable, and in fact natural. Planted tanks for example have a diurnal pH fluctuation of several decimal points, say from 6.0 to 6.5 during the day and then back again during darkness. There is no issue for fish in this, because it is what often occurs in their habitat waters and it is spread out over 24 hours and occurs slowly. So back to the internal pH, a fish programmed by nature to live in water with a pH of 4-5 is going to have to adjust its blood pH a lot to manage in a pH of 8. And many cannot do this. But as I mentioned earlier, the corresponding hardness is also of equal significance.