Dont try to get me to explain the science cuz I dont have a clue, but I half quoted someone else from another forum when i noticed it and asked too.
AS long as the stank smell isnt noticable, your filter should be sound. I was just in my room and i took some cuttings out of the tent that were in a propagator, just 1 minute out of the lights and in the dimly lit room, i noticed them stinking shortly after, I think when they rest, if theyve had more light than they need, they relerase oxygen and stink of Chlorophyll.
Just my 2 pennies bro.