Fluval FX4 canister filter pads

[JanetMoran]

I purchased ammonia, phosphate and nitrates pads for my canister filter. I’m curious as to where I should put them in my Fluval FX4 filter?

 

[Essjay]

The ammonia pad should stay in the cupboard. Rather than replace it before it gets full, forever, it is much cheaper to grow a colony of bacteria to remove ammonia. The pads remove ammonia so the colony of ammonia eaters can't grow properly, then there's not much nitrite made so the colony of nitrite eaters doesn't grow properly either.
Alternatively, use live plants to remove ammonia.