What is the right pH for discus and does it really matter?
Oh, yes, it does! There are relatively few fish species that are more sensitive to pH than discus. Do not be deceived by those assuring you that as long as the pH of your aquarium water is stable it does not really matter what it is. If you want to be successful in keeping healthy discus you need to learn about the pH of water and about the factors that affect the pH values. I kept all kinds of tropical fish species and bred them successfully for two decades thinking that I understood water chemistry well.
Then the first group of discus entered my tanks and they laughed out loud at my ignorance and lack of knowledge. The laughing did not last long, because, the pH of my water was very stable and very deadly for my discuss. The first batch of discus I had were not happy. They suffered for over a year until the stable and deadly pH of my water served to them long and painful death.
Here is the thing – pH is a slow killer in most cases. It is only the extreme values of pH rarely seen in aquariums that will kill your fish quickly. The typical range of pH of somewhere between 7 and 8 will kill your discuss very slowly over a period of many months, and you will not be even aware of the fact that it was the wrong pH that killed your discus.
To illustrate this better, let me share with you an analogy – does it really matter for us, human beings if we leave at the sea level or very high in the mountains? Many will say it does not, they love the beach, but they not mind the mountains. While this may be true for many people, it is a scientific fact that with increasing elevation temperature declines. The same is true of oxygen saturation in air. If you climb very high in the mountains, first you will start to get cold. As you climb higher you will enter elevations where snow cap is present even in the summer. At this height it is difficult for us humans to survive for a long time. The most extreme example is Mount Everest and the brave people trying to reach its summit. They all know that they need to reach the top quickly and equally quickly descent down to minimize time spent in deadly conditions. The cold and lack of oxygen will kill them if they stay there for too long.
Exactly the same it true for the pH of the water in your discus tank. Your discus may be ok at high pH for a limited time, but it you make it permanent condition for them it will kills them.
There is an ideal pH for discus and there are pH values that create very risky environment for your discus, with some extreme values that will quickly kill your fish if put under these extreme conditions.
Considering all this what is this ideal pH for discus? Based on my experience the perfect pH for discus, surprise, surprise, is exactly the same as in the water in their native environment, the Amazon River. And this is somewhere around pH of 6.5.
Any other value of pH, and especially if it becomes alkaline, will kill your discus. It will do it in many different ways. First, if the pH value falls within the danger range, it will irritate the mucous membranes and stress the immunological system of the fish. Then, once the defense system of the fish is weakened, the bacteria that flourish in alkaline water (and there are the types of bacteria that discus never evolved to co-exist with) will start causing problems for the homeostasis of the fish. This will sooner or later lead to bacterial and protozoan caused diseases.
In other words, do not expect your discus to be happy on Mount Everest. You would not enjoy living there either. Give your discus the comfort of a cozy home of a pH of around 6.5.