I explain with J what I do is move from 0 to 19 in the eeprom osea saving from 0 to 19 in the eeprom values
That would be the case if a value other than 0 ever appeared between the square brackets. As it doesn't, you might as well make j a scalar variable (non-array).
If you want to store values are each of the 20 positions in the array, you have to use all the values from 0 to 19 in the square brackets, or use a variable that takes on all the values from 0 to 19.