Importance of GH over pH in Freshwater Fish Aquaria

Byron

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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):

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.
 

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Really excellent post and interesting read. I'd be really interested in a similar set of tests being done on fish that have a really broad distribution like the X-Ray/ Pristela Tetras which are found in a variety of locations thoughout the seasons from some blackwater into more coastal waters too.
 

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Thanks for posting this.

I have spent the majority of my time since finishing work reviewing this. If I would summarize your statements it would be as follows
  • KH, carbonate hardness, primarily determines the buffering capabilities of the water to changes in pH. It is a measure of the carbonate and bicarbonate ions in the water. The higher the KH the more resistant to change in pH the water will be, though likely the pH will be somewhat higher in water with a high KH. To adjust pH of the water you have to consider both the initial pH and the KH of the water.
  • GH, general hardness, is effectively the amount of dissolved metals in the water, in particular Ca and Mg and can influence the well being of the fish. The example being the report on Paracheirodon axelrodi raised in water with elevated GH ended up with effectively kidney stones. Whereas other fish, like some African Cichlids prefer a higher GH.
  • Because the fish evolved in a particular set of conditions one can assume that they will do best in similar conditions.
I wasn't able to find any contradictory literature to any of your points, although the paper, "The Adaptions of Fish to Extremely Alkaline Environments" suggest that some fish are able to adapt to higher pH values. The paper also indicates that one issue with fish in water higher than their ideal pH is the with ammonia waste removal through the fish's gills, the main issue being at higher pH the partial pressure of NH3 in the water is higher resulting in higher NH3 in the blood serum of the fish. I haven't found any literature stating what happens to fish when placed in water with a lower pH than their ideal pH

The Adaptation of Fish to Extremely Alkaline Environments
 

itiwhetu

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The easiest way to avoid an ammonia spike situation is to run tanks slightly acidic, therefore I will always test for pH over hardness.
 

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Would you keep hard water fish (eg Rift Lake cichlids) in a pH under 7? Or have you always kept soft water fish?
 

itiwhetu

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African cichlids need hard water and an alkaline tank just as live bearers prefer slightly alkaline water, but the majority of fresh water fish do better in slightly acidic conditions.
 
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Thanks for posting this.

I have spent the majority of my time since finishing work reviewing this. If I would summarize your statements it would be as follows
  • KH, carbonate hardness, primarily determines the buffering capabilities of the water to changes in pH. It is a measure of the carbonate and bicarbonate ions in the water. The higher the KH the more resistant to change in pH the water will be, though likely the pH will be somewhat higher in water with a high KH. To adjust pH of the water you have to consider both the initial pH and the KH of the water.
  • GH, general hardness, is effectively the amount of dissolved metals in the water, in particular Ca and Mg and can influence the well being of the fish. The example being the report on Paracheirodon axelrodi raised in water with elevated GH ended up with effectively kidney stones. Whereas other fish, like some African Cichlids prefer a higher GH.
  • Because the fish evolved in a particular set of conditions one can assume that they will do best in similar conditions.
I wasn't able to find any contradictory literature to any of your points, although the paper, "The Adaptions of Fish to Extremely Alkaline Environments" suggest that some fish are able to adapt to higher pH values. The paper also indicates that one issue with fish in water higher than their ideal pH is the with ammonia waste removal through the fish's gills, the main issue being at higher pH the partial pressure of NH3 in the water is higher resulting in higher NH3 in the blood serum of the fish. I haven't found any literature stating what happens to fish when placed in water with a lower pH than their ideal pH

The Adaptation of Fish to Extremely Alkaline Environments

I agree with all you've stated here, absolutely. I have been digging for more scientific studies, and didn't yet come across the linked article, so thank you for that, I will read it and provide any observations later. But the bold statements here are without question bang on the mark. The book I mentioned in my post in the other thread, The Manual of Fish Health, emphasizes these very points (among some others obviously).
 

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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):

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.
Thoroughly enjoyable read as always Byron, thank you. I would love to hear your take on the importance of temperature regulation too
 
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Really excellent post and interesting read. I'd be really interested in a similar set of tests being done on fish that have a really broad distribution like the X-Ray/ Pristela Tetras which are found in a variety of locations thoughout the seasons from some blackwater into more coastal waters too.

I have some observations on this that may be of interest.

First, this species has as you've noted a wider distribution than most species in South America (the Serpae or Red Minor Tetra, Hyphessobrycon eques, is another that comes to mind, and interestingly has much the same aspects) and not only geographically but environmentally it can be found from soft acidic water to more basic and even in brackish along the coast. Pristella maxillaris occurs throughout the basins of the Amazon and Orinoco river systems, and coastal river drainages of the Guianas. Found in calm coastal waters and in densely vegetated swamps inland.

Second point to note is that the fish do not move from one of these habitat types into another, aside from the coastal populations that move inland to spawn. This means that the population that has evolved in a blackwater system remains there all its life, and has no need to adjust. Same for the other geographic populations, they are in a sense static. Most of the water basins in Amazonia are today geographically cut off from each other, but this was not always the case. The Amazon flowed west initially, at the breakup of Gondwana during the Jurassic era some 180 million years ago that lasted until the Eocene era. As the Andes were pushed up by the Pacific plate as what we know as South America moved west, the course of the Amazon and its entire basin changed direction, and geographical divisions became fixed. The ancestors of the SA characiformes evolved within these geographically isolated populations; phylogenetic analysis of many species such as Carnegiella marthae have discovered three distinct lineages within the separated populations, and two lineages for C. strigata; with respect to the latter species (Marble Hatchetfish) it has been found to overlap in one geographic area, but so far there is no evidence of cross-breeding between the two lineages.

When in 1995/6 Dr. David Sands discovered and described several Corydoras species similar in appearance to C. adolfoi, and found each to be endemic to specific tributary streams on the north bank of the Rio Negro, in his article he opinioned that one reason these distinct species did not migrate to adjoining streams when not prevented by land was perhaps the "barrier" posed by the substantial difference in water between the Rio Negro and the various tributaries. The fish evolved to "x" parameters, and given the option that is where they remain. This would tend to be further proof of the benefit of providing as close an environmental habitat as possible, thus avoiding additional stress and metabolic problems..

Third, this obviously raises the question then as to why the commercial Pristella maxillaris fish are so adaptable. For decades this species has been commercially raised. Chances are the original fish came from more "basic" habitats easily accessed, so they manage in moderately hard water very well. Their physiology so far as I understand is still that of a soft water species so they are able to do well in softer more acidic water. Suggested water parameters are in the ranges of soft to slightly hard (hardness to 30/35 dGH), acidic to basic (pH up to 8.0), with temperature 24-28C/74-82F. In hard water it will not be as colourful, which is another clue to the above.
 
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Another piece of evidence comes from the late Dr. Jacques Gery, who during the last half of the previous century (the 20th, to be clear) was acknowledged as the authority on the characidae; his book Characoids of the World (1977) is still a primary reference tool. I can't track it down, but in one article he noted that aquarists manage to keep the cardinal tetra alive for maybe three to five years. But maintained in very soft water, it will easily live beyond ten years. Opinions really don't count much without the scientific data to substantiate them, but with a scientist of Dr. Gery's stature opinion is inevitably science. Heiko Bleher in his obituary of his close friend said that you could name any watercourse and Jacques could tell you all the fish species native to it without looking them up.
 

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This is all very interesting, but is about wild fish in natural habitats. I will continue to promote the idea that in Aquaria it is important to aim for slightly acidic conditions, therefore testing for pH is vital. Ammonia is the biggest killer and stress provider for freshwater fish and the easiest way to prevent ammonia in Aquaria is have tanks that are slightly acidic.
 
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Byron

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This is all very interesting, but is about wild fish in natural habitats. I will continue to promote the idea that in Aquaria it is important to aim for slightly acidic conditions, therefore testing for pH is vital. Ammonia is the biggest killer and stress provider for freshwater fish and the easiest way to prevent ammonia in Aquaria is have tanks that are slightly acidic.

First, the habitat conditions tell us what the fish requires to be in good health, assuming that is our goal--healthy fish. Acidic conditions is fine, ideal in fact, for soft water fish. But you cannot keep hardwater fish in soft water without causing them internal problems, leading to a shorter lifespan whether from those problems or from other health issues they cannot fight off due to the weakened state from the inappropriate water parameters.

As for ammonia...in a balanced healthy aquarium one should never se ammonia at levels that can harm fish. Floating plants alone will ensure this. And good maintenance and husbandry.
 

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