I've never noticed any yellowing. I also wouldn't understand why anyone would scrape it in the tank. The point of the ATS is to remove the nutrients from the water, if you clean the scrubber in the tank, you are just releasing organics back into the system which would defeat any purpose of running the ATS to begin with. You're supposed to remove the screen and clean it. The only reason I could think people would clean them in the tank is laziness.






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