Ok, I don;t kow if this will wrok as I have not actually done this and I hate undergravel filters but why not set up a reverse flow UGF
? This will prevent anything from falling to the bottom because of the upward flow forcing all the mulm and gunk to stay in the water column si it can be removed by either prefilters on the powerhead, AC110 or Rena XP3?
This would cover the entire tank and notjust certain location, make it a lot easier than tryin to plumb and adjust 6 flow rates and might look better.
That is off course assuming that the substrate is not sand or extremely small and that you don't have large rooted plants, if you do, just ignore me, lol.