Run off system

Hi guys, I am growing in coco and I've got a medusa run off system and it pumps the run off out into a bucket outside of the tent and the run off stinks like farts lol. I'm guessing it's due to stagnant water. I've ran a load of water through the main brains with the pump in and through the saucers that catch the water to try and get rid of the stagnant water but after a day or two it starts stinking like farts again lol. Any help is appreciated

Here is a video of the run off system I am using