nitrates wont go down

You should do a little research on algea turf scrubbers they have been proven to lower phosphates and nitrates, I have one on my tank and love it, they are easy to setup. I have also read that seachem's purigen will reduce nitrates, I have no experience with purigen though. In my experience with fowlr tanks no amount of water changes, deep sand bed, bigger skimmer, more rock, less feeding, nothing brought the nitrates down but the algea scrubber did. You could set on up and see how you like it, if you like then when you setup your next tank I would take out the bioballs and the pre filters. The reason I say take out the prefilters is because you dont clean them once a week they are nasty and will build up your nitrates. If you want to run carbon it would be better in a reactor and depending on how much your using change it every two weeks.

 

Just as importantly as loosing the bioballs is

LOOSE THE SPONGE FILTERS!

Agree with pretty much everyrthing that has been said, including perhaps the ATS- never used one myself though.

40-80? Wow, I mean wowsa!