Short answer: pH range is 5.24 - 6.95, and temperature is 22.1 - 31.9 degrees Celcius.
Recently, I was perusing a journal article and found, to my surprise, that the pH ranges listed for various Betta species were significantly lower (and broader) than what is often suggested. Chances were that temperature ranges differed, too.
So I decided to collate data on pH temperature from betta care guides and compare them to literature to determine how close to 'natural' the ranges listed were. I do want to stress that:
I only limited my search to Betta splendens as this is the most common betta 'species' in the hobby, although plenty of individuals are probably hybrids,
Despite having checked over a hundred articles, I have not checked and cannot check every single journal article out there,
Just because ranges for a variety of locations have been identified does not mean that they are representative of the pH/temperature range of all natural environments that B. splendens live in, and
There is no evidence that a species can only thrive in their natural habitat's pH/temperature ranges.
So, this guide to the pH and temperature ranges should only be for reference's sake. Aquarists have reported keeping bettas in water with pH >8 in aquaria, and their fish still did well. And again, importantly, there is no guarantee that your betta is pure B. splendens, either. It should also be noted that what constitutes a 'natural environment' may vary in definition from researcher to researcher.
Alrighty, without further ado.
I identified three journal articles that listed pH and/or temperature ranges for B. splendens:
Location | Low pH | High pH | Low temperature (Celcius) | High temperature (Celcius) |
5.24 | 6.95 | 26.6 | 31.9 | |
5.4 | 5.8 | 22.1 | 25.1 | |
5.28 | 5.8 | 27 | 31.5 |
The high end of the pH range for Aceh is much higher than that of the Thai regions. There was one of the five locations in Chiang Rai that had a low-end pH of 4.8. As this was an outlier, it was ignored here. The temperature range across all locations was between 22.1 to 31.9 degrees Celcius, though the intra-regional difference was only at most 5.1 degrees Celcius.
Therefore here, the pH range is 5.24 - 6.95, and temperature is 22.1 - 31.9 degrees Celcius. Again, this is a reminder that this range is not necessarily reflect of ALL natural environments that B. splendens live in.
Only Seriously Fish listed a low pH similar to the studies examined, at 5 vs. 5.24. Aquarium Source, LiveAquaria, Bettafish Forum, and Beta Care 101 are next closest at 6, but still quite a bit higher. All other guides are significantly off. In terms of high-end pH, only wikiHow has a similar number listed. Broadly, it is clear that B. splendens comes from environments with much lower pH compared to what is often stated in care guides. I did try to find at least one journal article that stated a high-end pH higher than 6.95, but could not. At this stage, I am unwilling to suggest bettas must not be kept at a pH above 6.95, rather just that bettas are happy in much lower pH than what aquarists commonly think.
Here, only Seriously Fish lists a low-end temperature similar to that B. splendens found in the wild, though none of the guides approached close to the maximum temperature in nature. However, it should be noted that temperature maxima in the wild may only be temporary, versus what is the larger range of temperature year-round. Regardless, it still suggests that bettas should be happy in temperatures much higher than what many of the guides suggest. After all, B. splendens in Aceh and Nakhon Si Thammarat are pretty much always subjected to temperatures higher than the highest recommended by Fishkeeping Advice, Buce Plant, and r/bettafish (26.7 degrees Celcius).
There we have it, folks. So far, the journal articles I found list the pH range as generally lower than in betta care guides. Meanwhile, the temperature range is broader.
What you do with this information is up to you though, but I suppose the gist of the message is, bettas are probably far hardier than generally assumed.
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