Phosguard for Fluval Evo 13.5gal

[saltlife26]

Hello all. I want to get a 100 ml bag of Seachem Phosguard for my tank. Currently I am using the stock setup which comes with the foam filter block with two compartments- I have carbon in one and biomax in the other. So my question is, where do I put the bag of Phosguard? Thanks

 

[AdamNC]

Where ever water can flow through the bag preferably after the foam block.