StarSan life in a spray bottle

[berheidebrau]

Anyone got an idea how long StarSan solution lasts in a spray bottle?
I'm checking gravity everyday or two with a thief from a carboy and would rather not have to make a new solution each time. I suppose I could check the ph but I guess I want less steps as possible!

Thanks!

 

[FloppyKnockers]

'Til it's gone.