Aquarium - measuring spoon for Sodium Bicarbonate

I made a spoon to dose the Sodium Bicarbonate easily. I use it to raise the KH of the tap water when I do the water changes in my aquariums.
My tap water isn't hard enough and I have to raise the carbonates in it.

I use 0,3 g of Sodium Bicarbonate every 5 liters of tap water (previously conditioned).
It usually raises the KH by 1 degree in a few hours.

This quantity of sodium is not a problem for the fishes or the shrimps.