The only info I have on how long it lasts is based on my own experience (using it in canister filters on salt tanks), mostly gleaned from my days doing maintenance and at the shop. Rinsing it prolongs its life (if I think there's a heavy load then I may rinse weekly), but then I have also not had a problem with yellowing water, not even with Caulerpa, that I've had to address with carbon (specifically in salt), so I can't speak directly to that. Other than that, I go with what my former supervisor at LBAOP was doing, leaving a bag of carbon in the sump of the coral lab's sys, rinsing monthly. The water isn't being forced through the carbon, so it isn't being "taxed" (?) as much as something being used in a closed loop/pressurized filter.
The yellowing issues I've had to deal with were with f/w sys's, mostly those using peat for softening and acidifying, or with much organic matter, such as planted sys's.