But to what degree? That's what I want to know.
I used a HOB for a while, and the filter pad already had carbon in it. I dosed macros and Excel and didn't see it adversely affect my tank. Of course this can depend on how old the carbon is (usually isn't good anymore after 2 weeks, sometimes less) and how much there is compared to tank size. But generally speaking, from my experience, it doesn't adversely affect plants.