Would lowish PH cause fish deaths

[Bruce Leyland-Jones]

@imw I really am sorry about the confusion you are experiencing. And I am familiar with your other thread on the fish deaths (which I sorted out therein as to the actual cause).

Unfortunately, pet store employees are not trained (for the vast majority of stores, there are some hobbyist-run stores but they are rare) in fish physiology, habitats, and requirements. Many of us will say the same--do not rely on their advice, ever. If I had listened and accepted much of the "advice" I have received from store staff in years past, I would not be in this hobby now, solely out of frustration with the lack of success that would have followed this inaccurate advice. Research and only research should be your guide, and that includes a forum like TFF.

The Penguin Tetra, which is probably the species Thayeria boehlkei as this is the most commonly seen of the three species in this genus in the hobby, occurs (its natural habitat) in the Rio Araguaia in Brazil and the Peruvian Amazon. The waters in most of the Peruvian Amazon area are acidic (pH well below 7 for most, certainly not above) and very soft (zero GH). The parameters for the Rio Araguia are pH 5.8-7.5 (6.5), 4-20 dH (8), 72-82?F (22-28?C). Early dry season pH would be 7.0 (6.7-7.3), the late dry season 6.9 (6.6-7.0). Unlike the other two species (T. obliqua and T. ifati) in the genus, this species can be maintained in slightly basic (alkaline) water aquaria but it is not necessary. The fourth species, T. tapajonica, was only described in 2017 and is very unlikely to be common in the hobby.

Soft and somewhat acidic water is ideal. This will not cause "fish deaths" unless the fish are species requiring harder water (with a basic pH to match), such as livebearers.

Great info for wild-caught fish, but what about those reared in farms elsewhere?
Whilst I wholly accept each fish contains a genetic componant, allowing it to thrive in its home environment, each fish also contains genes that facilitate adaptation to changing water conditions.
Farm-bred fish are used to very different waters, then placed in a small bag in which they exist for thousands of air miles and are then placed in the water of a fish shop. Those that survive this ordeal, may well do quite nicely, once acclimatised, to waters consistent with those experienced by their ancestors...or they may not.
Discus are a great example of how breeding in fish farms can change the requirements of a species.

 

[Byron]

Great info for wild-caught fish, but what about those reared in farms elsewhere?
Whilst I wholly accept each fish contains a genetic componant, allowing it to thrive in its home environment, each fish also contains genes that facilitate adaptation to changing water conditions.
Farm-bred fish are used to very different waters, then placed in a small bag in which they exist for thousands of air miles and are then placed in the water of a fish shop. Those that survive this ordeal, may well do quite nicely, once acclimatised, to waters consistent with those experienced by their ancestors...or they may not.
Discus are a great example of how breeding in fish farms can change the requirements of a species.

I won't get into a discussion about whether or not fish requirements can change, that is another story. I understand from several biologists that a fish, regardless of the tank/commercial breeding, will always fare at least as good if not better in parameters for which it is designed. So that is always a good starting point. [See The Manual of Fish Health, authored by Adrian Excell, Dr. Chris Andrews, Dr. Neville Carrington, and Dr. Peter Burgess.]

Most if not all of the soft-water fish available in North America are (if not wild caught) raised in SE Asia, in soft to very soft water, in outdoor ponds. So they are coming from the same basic water as the natural habitat of the species. I'm dealing with soft water species here, which is what the subject fish are. I've no idea if this is the same in the UK.

Fish can tolerate water differences short term (usually), but long-term is a very different thing, so store water is something of a red herring as the fish don't normally stay in it long enough to develop issues.

I did point out that the subject species had a wider range than the two other species in the genus. But that does not make the advice from the store that they must have basic pH, that is absolutely false. And I know of no soft water species that will not live, even thrive, in soft as opposed to hard water. This rubbish about fish must have a neutral pH is just that, rubbish. Livebearers and other moderately hard water species, yes, absolutely. But not soft water tetras.