I removed all the bio media and washed it out. Unlike what you are thinking,it's just a minor setback for the bacteria. Because that media ( old,old,course floss and 15 gallons of it or more) gets dirty it can make the rinse become a deep ink black. I wash it to coffee with cream color. Nope,never toss it out or wash until it's got no tint. A cream is a good color.
The floss? Lasts for years.When its new,you don't need as much..its fluffy. As time goes by? It's not so fluffy and then I just add more to the filter..as more time goes by? Its set. Since it never rots,I imagine what breaks down into gas is a slow process.
I had to top off with about 10 gallons of water from the evaporation since last week,dosed potassium and two shots of Seachem Iron. When all is clear,I think I will use a sock full of carbon,and remove the slight tint without removing ( I think) the good stuff for the plants.
I've NEVER done this..try the no water change plant aquarium but as the weeks go by and most everything is looking better?...cant say when I will make a water change.