Natural means – als alder cones, beech and oak leaves – that could replace peat are very good, but often have a weak influence on pH only. But they deliver humid substances to the tank water, and that is nearly as necessary as the pH itself.
But our fish are accustomed to low pH-values by their evolutionary history. Again I repeat what I have said very often already: Not the pH is the decisice factor but the consequence it has: a low concentration of germs. That is the central point. Especially the eggs and larvae of our fish don’t stand the normal concentration of germs in a normal (“clean”) aquarium water. This concentration is a hundred or thousand times more than in nature, although everything looks clean.
The aquarist has only one means of influencing this markedly, and that is by lowering the pH. Which sort of acid you use is a secondary importance. Sulphuric acid is just as effective as other acids.