HI, I would take the foam out of the Fluval 404 to hard to clean every few days.
The food it will trap, will eventually cause more harm then good...
Use your other filters that are easier to clean every few days...
Save your money for more live rock it's cheper then carbon in the long run.
I read somewhere that carbon in saltwater is only good for about 3 to 4 days!!
If you'd like to check out "the new marine AQUARIUM" a book by Michael S. Palette. may enlighten you on how LR