The minimum threshold for income tax (known as "ganancias") is adjusted upwatds for inflation regularly. It is currently 2.4 million pesos per month (about US$1800, at today's exchange rate, which also moves around quite a lot of course) for a single person with no dependents. If your pension is less than that, the double taxation problem doesnt arise. (The amount is currently very close to the amount you have to have to qualify for tge Pensionista temporary residency.)
The problem also doesnt arise until you become an Argentine tax resident: after 12 months with temporary residency issued by the Direccion Nacional de Migraciones (although if you spent 90 days in every 12 months outside Argentina you can defer tax residency three years to the date you become a permanent resident).