ABS fluid reservoir should be translucent, so with the right light you should see the fluid level just like your main brake-fluid reservoir. (wipe the crud off the outside of the ABS reservoir)

 

Ok I wiped the crud off and found just the opposite of low.

The Reservoir has a Max Line about half way up the Reservoir and the fluid level was up to the top of the Reservoir. What does that mean.

 

That probably means someone over-filled it. But that doesn't rule out the possibility that there's air in the ABS modulator, or for that matter air in the main brake system. Bleed your brakes & see whether that helps.