In another thread, I was asked by @Uberhoust if I had scientific data to support my frequent advice that GH was the more important parameter when compared to pH [temperature is another critical parameter but outside this particular discussion], and rather than hijack that thread, perhaps start a discussion here. So, here I am, (hopefully) with some evidence.
I am going to begin by pointing out that attempts to adjust the pH on its own are almost always worse than leaving it alone--unless you go about it the correct way. And that begins with the GH (general or total hardness) and KH (carbonate hardness, also termed Alkalinity by some). The GH and KH act to buffer the pH, preventing any changes, depending upon the level of GH/KH. This is why you must first ascertain these levels in your source water. Usually the higher the GH/KH, the higher the pH, but not always. But I can guarantee that if you ignore the GH/KH, and it happens to be high enough to effectively control the pH, all your additions of chemicals to lower the pH will only stress the fish and eventually kill them.
Now to a consideration of how GH affects fish.
First, a synopsis of a study reported a couple decades ago, but the age is irrelevant as we are dealing with scientific evidence/fact in the data. It was an article in Tropical Fish Hobbyist, August, 1987, pp. 66-87 [yes, lengthy, a lot of data/information], entitled "Ecology of the Cardinal Tetra, Paracheirodon axelrodi (Pisces, Characoidea), in the River Basin of the Rio Negro, Brazil, as well as Breeding-related Factors," authored by Rolf Geisler and Sergio R. Annibal. This article is important for other aspects of cardinal tetra care such as their extreme light phobia (they avoid waters that are not deep dark) and their avoidance of flowing currents whenever possible, but these factors will have to wait for another post!
The reference to parameters began with collection data of the species' habitats along both north and south tributaries of the Rio Negro. The authors defined typical blackwater streams in the catchment area of the Rio Negro as follows:
pH <4.3
Ca (calcium) and Mg (magnesium) < 1 mg/l [mg/l = ppm]
and they continue: "If all the limnochemical findings available from P. axelrodi biotopes are evaluated, the following water composition arises:
pH values 3.97 - 5.1
Total hardness 0.00 - 0.03 dGH
There is very worth-while data respecting the pH as a controlling factor in the habitat sources of P. axelrodi; it largely avoids or is found in greatly reduced numbers in waters having a pH below 5, and the authors conclude that this is not a "typical" black-water species if such fish do actually occur. But it is the GH that is behind this post, and there is some convincing data. Citing direct from the article (p. 79):
The article goes on to mention that breeding strains in the USSR over the previous several years have had success breeding this species in harder water, up to 12 or 15 dGH. It dos not delve further into this.
Hard-water fish species have a sort of opposite problem. Thy must have calcium (primarily) in the water, at sufficient levels to provide them with the minerals essential to the operation of their internal life processes. Like their soft-water cousins, they evolved in very specific water, and in their case it is mineral-rich, so their physiology evolved to function in such water. It might be that the GH level is of more importance to hard-water fish than soft. But it is certain that a very low GH (amounting to very soft or soft water), regardless of the pH, is not going to provide a healthy life for such fish. I will get into this more in a subsequent post.
I am going to begin by pointing out that attempts to adjust the pH on its own are almost always worse than leaving it alone--unless you go about it the correct way. And that begins with the GH (general or total hardness) and KH (carbonate hardness, also termed Alkalinity by some). The GH and KH act to buffer the pH, preventing any changes, depending upon the level of GH/KH. This is why you must first ascertain these levels in your source water. Usually the higher the GH/KH, the higher the pH, but not always. But I can guarantee that if you ignore the GH/KH, and it happens to be high enough to effectively control the pH, all your additions of chemicals to lower the pH will only stress the fish and eventually kill them.
Now to a consideration of how GH affects fish.
First, a synopsis of a study reported a couple decades ago, but the age is irrelevant as we are dealing with scientific evidence/fact in the data. It was an article in Tropical Fish Hobbyist, August, 1987, pp. 66-87 [yes, lengthy, a lot of data/information], entitled "Ecology of the Cardinal Tetra, Paracheirodon axelrodi (Pisces, Characoidea), in the River Basin of the Rio Negro, Brazil, as well as Breeding-related Factors," authored by Rolf Geisler and Sergio R. Annibal. This article is important for other aspects of cardinal tetra care such as their extreme light phobia (they avoid waters that are not deep dark) and their avoidance of flowing currents whenever possible, but these factors will have to wait for another post!
The reference to parameters began with collection data of the species' habitats along both north and south tributaries of the Rio Negro. The authors defined typical blackwater streams in the catchment area of the Rio Negro as follows:
pH <4.3
Ca (calcium) and Mg (magnesium) < 1 mg/l [mg/l = ppm]
and they continue: "If all the limnochemical findings available from P. axelrodi biotopes are evaluated, the following water composition arises:
pH values 3.97 - 5.1
Total hardness 0.00 - 0.03 dGH
There is very worth-while data respecting the pH as a controlling factor in the habitat sources of P. axelrodi; it largely avoids or is found in greatly reduced numbers in waters having a pH below 5, and the authors conclude that this is not a "typical" black-water species if such fish do actually occur. But it is the GH that is behind this post, and there is some convincing data. Citing direct from the article (p. 79):
Investigations by G. Schubert on young P. axelrodi caught in April, 1982, in the Igarape Mamole-Rio Cuiuni and brought to Germany in the original water provide an important clue. At the Hohenheim Zoological Institute some fish were put into a mixture of water from Lake Constance and completely salt-free water in the ratio of 1:9. These fish, after only 7 months, showed a more or less pronounced blockage of the kidney tubuli with amorphous, strongly refractive matter. Calconephrosis is suspected. When 4 more animals were dissected at the end of June 1983, the blockage of the kidney tubuli had become very severe.
The article goes on to mention that breeding strains in the USSR over the previous several years have had success breeding this species in harder water, up to 12 or 15 dGH. It dos not delve further into this.
Hard-water fish species have a sort of opposite problem. Thy must have calcium (primarily) in the water, at sufficient levels to provide them with the minerals essential to the operation of their internal life processes. Like their soft-water cousins, they evolved in very specific water, and in their case it is mineral-rich, so their physiology evolved to function in such water. It might be that the GH level is of more importance to hard-water fish than soft. But it is certain that a very low GH (amounting to very soft or soft water), regardless of the pH, is not going to provide a healthy life for such fish. I will get into this more in a subsequent post.
