When to Refill Calcium Reactor Media

[JAMSOURY]

At what point do you refill your calcium reactor media after some has been depleted?

 

[X-37B]

I think mine says when 30% has been used if I remember.
My carx is small.
The media chamber is 4" round by only 8" tall.
I added media when it dropped 25% or 2".
Some people go quite a bit lower.
Here is a pic when I added media.