bio

So I'm sitting here looking at my XY dual sponge filter... ...and I just finished watching and reading up on "Fluidized Sand Bed Aquarium Filters"... ...when it struck me that the little clear tube looked very much like a FSB sans the media...and that "De Nitrate" was supposedly designed to...

I bought more than I need so I'm selling two one 1 Liter bag (2 liters total) of Ehiem Substrat Pro (new, sealed in original bags). SOLD

I have two 2215 filter and I remember reading somewhere that it's recommended that you replace 50% or so of the bio media (ehfisubstrat/pro) every year or every so often. I was wondering what's the reason behind this. Is it only because the pores of the media get clogged up or is there another...