Media bags in overflow box?

My custom made overflow box is quite wide and with some limited room in my sump, I thought about putting a media bag with either phosphate reducer or carbon in there. Any reason this wouldn't be feasible?

 

You can do it, but it can be somewhat risky. For those media to work best, water needs to be forced through them. So, you'd want to place it in such as way that water is forced through it before going down the drain. If it gets clogged up though, your tank could overflow. Also, the flow rate is probably too high and the optimal flow rates for GFO and GAC are different. You could just let it sit there passively, but that won't be very effective.

 

How about placing a small pump to run a reactor which would hang on the back?