I'm fairly certain its disclosed somewhere that light is just on a timer, there is no realistic way to monitor something like that otherwise. Depends on your t

I'm fairly certain its disclosed somewhere that light is just on a timer, there is no realistic way to monitor something like that otherwise. Depends on your tank, see "how do I read and reset" https://www.brita.com/support/faqs/replacement-filters/ https://www.brita.com/support/faqs/replacement-filters/