400 gallon filtration upgrade help

anyway of setting up a sump under the tank?

If you have the money......

I would go with at least a 75 gallon tank... but preferably twice that. You could do it pretty cheaply by finding the tank used and filling the wet/dry drip portion with pot scrubbers. Otherwise, you could always add another canister like the FX5. IMHO... the sump is the way to go with a tank that size.

When you say that you have too much trouble with keeping up with the levels... Do you mean that the nitrates are building up too fast, or are you having problems with the ammonia and nitrite building up? If the nitrate is building too fast, either you have too many fish, feed to much, or you aren't doing a large enough water change. I personally do 50-75% water changes on my tanks weekly. If your ammonia and nitrite are building up fast, that means you need more bio filtration. In which case you could add something easy like an AC110 or two, or an emperor 400 or two. If it is the latter problem, GET FILTERS FAST.

it depend's on how much space you have under your tank?. Go for as big as possible, my sump is 60"long x 24"wide x 15"high, with the middle partition being 24"x17" to fit pond sponges, the pack of 3 different grade one's. load's of bio tubes and then 6 sponges on top of that.

also i have a R.O. unit on my tank constantly, and i beefed up the filtration with a FX5 .

Any chance of some pic's of your tank?

Kev