Okay... I've stayed out of this whole UGF thing before but... Have you guys
ever thought about setting up the UGF this way:
Place a layer of poly batting which comes in rolls (used for quilting and
stuff) on top of the plates and tuck it under the plates. Then add laterite
or whatever and then normal substrate over that. Cut Xs where the tubing
needs to come out of the plates and slide the batting over it. The batting
keeps the laterite from getting into the powerheads or whatever you use to
drive the UGF. I personally used this method when I set up an undergravel
filter and never had a problem. I used peagravel over the batting, then
laterite and then sand on top. When I finally moved and broke the tank down
the batting was serving as a biological filter and a fertilizer layer for
the Amazons... they had roots all through the batting so I guess that's
where all the nutrients were being caught and that's where the sword's roots
stayed. I plan to use this method again someday but right now I'm just
depending on my Fluval 304.