You stated in an earlier post that you use tap water & recommended against using peat. Do you use anything to soften the water & lower general hardness ( calcium & magnesium ) ? What is your opinion on the water softening pillow ( soaks up calcium & magnesium ions & replaces with sodium ions. Thank you for sharing your experience & knowledge.
The discus fish can tolerate from pH 5.0 to 8.0
If the fish can live happily why do we want to lower the pH?
Unless for some purposes like breeding when the fish needs to be in that condition then we need to adjust it.
In our location in Malaysia we are lucky that the pH is around 6.0 to 7.0.
Practically we do not worry much about the pH. Only if we want to breed the wild strain we need to lower pH to 5.6
To lower the pH in natural way, soak some dry leaves to make water acidic to soften the water. Peat moss and softening pillow can help.