As already said it's not even a thing and physically couldn't be..
Imo carbon is just as effective in a filter bag.. I went all big and bad in my last build and had dual Mrc reactors ( gfo/carbon) and within 3 months I went back to just putting it ( carbon) into a bag in a high flow area like I have always done.. Been doing it for 18 years and will continue to do so.
Used the reactor for an add on chamber for my calcium reactor =)..
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