A pair of words that mean fast- and slow- changing

I'm looking for a pair of adjectives which mean, respectively:

• Fast/Frequently-changing
• Slow/Rarely-changing

As an example usage:

Due to its everyday use, the balance of a current account can be quite fast-changing, but that of a savings account is more likely to be slow-changing.

And as a demonstrative graph: the value denoted by the red lines is more fast-changing, whereas the green value is a lot more slow-changing. The size of the changes is irrelevant - only the frequency is of importance.

The best I've come up with is volatile for the fast-changing part (probably closest to the third definition at dictionary.com), but I can't think of a suitable antonym. To me, stable has more of a connotation of not changing very much when it does change, as opposed to not changing very often.

By contrast:

If the green and red graphs above are frequently and infrequently changing respectively, then the orange, blue and purple graphs are changing continuously (infinitely frequently) - they're all way off to the "frequently" end of the spectrum.

For your example, 'dynamic' and 'static' work:

Example: Due to its everyday use, the balance of a current account can be quite dynamic, but that of a savings account is more likely to be static.

dynamic adj.
...
3. Characterized by much activity and vigor ....

[dynamic. (n.d.) American Heritage® Dictionary of the English Language, Fifth Edition. (2011). Retrieved November 17 2015 from http://www.thefreedictionary.com/dynamic]

static adj.
...
3. showing little or no change ....

[static. (n.d.) Random House Kernerman Webster’s College Dictionary. (2010). Retrieved November 17 2015 from http://www.thefreedictionary.com/static]

What about "stable" instead of "static"? I can see why "static" won't do - it usually implies that there is no change whatsoever - but "stable" often implies that change is possible.

So - "dynamic" and "stable".