I've been interested in following this thread, since the OP and I have had an extensive discussion around his water parameters and fish species. And Ed has now made a couple of important points and I'd like to offer some further observations.
First, let me say that I did tell the OP that his present source water is not bad and will suffice for the fish he intends, and this is primarily because his GH is not high as one might expect with the pH hovering around 7.8 to 8. The GH was thought to be down around 2 dGH, though in our PM exchange earlier today it was mentioned that this may have been incorrect (the GH may be around 8 dGH) so another test will be done to confirm. But this is not bad either, given the fish.
The GH is actually the more important for fish, be they soft water or hard water. Fish are able to manage within a wider pH range (though this has limits) provided it is fairly stable, but the mineral content in the water (GH) directly impacts on their physiology. And in the case of soft water fish, the TDS (total dissolved solids, which includes GH) is also significant. Soft water fish have evolved to function best in soft water, and conversely hard water fish require the minerals to function properly. The physiology of each species is so designed. Dr. Stanley Weitzman has written at length about the necessity of specific water parameters for soft water species if one hopes to maintain them in their best health.
We must remember that a fish is a very unique creature, vastly different from all terrestrial animals. Four important body functions of its homeostasis are closely associated with processes in the gills: gas exchange, hydromineral (osmoregulation) control, acid-base balance [pH] and nitrogenous waste excretion [ammonia]. These processes are possible because of the close proximity of the blood flowing through the gills to the surrounding water, as well as the differences in the chemical composition of these two fluids (Bartelme, 2004). Each species of fish has evolved within a specific environment—and by “environment” in this context we mean everything associated with the water in which the fish lives—and the physiological homeostasis only functions well within that environment. This greater dependence upon their surrounding environment is why fish are more susceptible to stress than many other animals (Wedemeyer, 1996).
Homeostasis is defined as “the tendency of an organism or a cell to regulate its internal conditions, usually by a system of feedback controls, so as to stabilize health and functioning, regardless of the outside changing conditions.” Physiological homeostasis, or physical equilibrium, is the internal process animals use to maintain their health and life: “the complex chain of internal chemical reactions that keep the pH of its blood steady, its tissues fed, and the immune system functioning” (Muha, 2006). The physiology operates in conjunction with the water in which the fish lives, and the slightest changes to this water can have very significant impacts. Laura Muha authored a monthly column in TFH a decade or so ago entitled The Skeptical Fishkeeper, and more than once she compared this to a car being driven uphill; it takes more gas (energy) to maintain a normal speed travelling uphill as it does on level ground. And similarly, in a negative environment a fish must expend considerably more energy just to maintain the physiological homeostasis crucial to its life. The consequences of this are significant.
Generations of commercially-raised fish may have greater success in differing water parameters to those in which they evolved. Not all that much concentrated study has been done in this area, and with fish it is often very difficult to know how the creature is actually coping with the environment into which we force it. We do know that in time, all species evolve to environmental changes--or sometimes they die out and open the way to other species to fill their niche. But we should remember that just because the fish remain alive, this does not equate to being in the best of health. In the aquarium, a fish's lifespan can sometimes be used to gage their level of coping. The issue of calcium deposits in the kidneys of cardinal tetras was mentioned in an earlier post; a German study reported in TFH back in 1987 determined that the lifespan of this species was directly related to the calcium hardness of the water, and the higher the GH, the shorter the lifespan. They found that this fish could successfully be maintained in a hardness of 4 dGH, though without spawning occurring. The normal lifespan of ten years or more could not be realized in harder water. They also noted that after several generations of tank-raised fish, the species seemed to show less pronounced physiological requirements as far as water composition is concerned. As they surmised, it seems probable that many other soft water fish would have similar issues and results.
Byron.
