True and recent story. last week I received my broad spectrum fungus and bacteria fizz tablets and had a tank wide case of rot that I got introduced by an LFS chain where I bought 2 silver dollars.
A few days before receiving the Fizz tabs by mail I decided to clean out my FX5 as it had been running for 4 months non stop and decided since the carbon was only 4 months old I would give it a thorough massage and rinsing clean in both treated water and RO and then just placed it back into its basket resting on a layer of bio balls about 3 cups of carbon.
After finally receiving my meds by mail and dosing I noted one of the medications in the fizz-tab cocktail was MB (methylene blue) a substance I had used as a kid when that is about all they had back then in the 70's. I wasn't concerned because the carbon was old and theoretically ineffective and kept inside for its bio mass.
Well to my surprise knowing what and how MB remains and lingers in color and intensity without the use of carbon, the MB color only lasted for about 2 hours before the tank was once again crystal clear no doubt due to the carbon, which is a prime example of how life often contradicts theory.