Hi Abby, nice to hear from you again!

You do not need to remix the whole lot. Use the spoon to scoop enough for the day of painting and pot it in the separate container, leave the rest as it is (in the jar under the layer of water).

Add water as necessary and stir, you can regrind the pigment before adding water if you wish.

If water or pigment is imperfect it may go stale after a while. This is why traditionally for important (commissioned) frescoes pigments where ground fresh for each day. However you need a full size workshop with one ore two assistants to do it (there is no time for the painter to do it on his/her own)

For instudio, small frescoes and experiments, storing pigments as described in this topic is the way to go.
Just make sure that water is distilled, pigments are fresh and pure and came from the reliable sources.

ilia
ilia