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Recently Bob Dixton and Ed wrote about the use of reverse flow UG
Many plant hobbyist abstain from UG's for good reasons but in reverse
these do work very well . I  tend subdivide sustrates into 3 catagories
: No flow---osmosis only;Low flow----heating cables;High flow---reverse
flow UG's .Each has it's advantages and disavantages etc. I have found
over the years that the tube style RFUG's to work the best for me.Please
look up the following picture!
An example of this is on pg.15 of Aquarium Plants
--(Rataj/Horemanni).This "grid" is the recommended method for planted
tanks back when the book was written  and was sound advice.
I used them in AF cichlids and salt set ups before plant tanks .I now
use CPVC 1/2" or PVC. It cost about 5-10$ to make for any size tank. I
have used these set ups for 9 years now and I also have all three types
of substrate systems also but mainly for referances (and just in case !
But after doing these for a few years ,it's the "other" way around now.
     The big advantage with the RFUG's seems to be with never getting
any anaerobic problems and the tank being able to handle higher fish
loads. I've tried every plant I could find on this RFUG set up @
75gal/sq ft. flows with results that are the same as heat cables .I have
also used laterite,kitty litter,plant spikes,peat etc with great sucess
and suprizingly little cloudiness. Dosing laterite is a snap also
because it can go right into the input tube that goes beneath the
substrate were it's needed(? Perhaps only on new tanks IMHO). Flows can
be lowered and warm water can be injected or a heater can be placed next
to intake of the filter ,although this does not do much with the high
flow rates associated with RFUG's. I had the same idea and the gravel
would "hold" the heat better than water alone.
  Tunze had/has something called "Bio-irrigator" that is similar to this
RFUG. They stated that around the out flow ,there are areas of oxidation
and areas of reduction outside of this out flow. I spaced my holes in my
Tube Grid CPVC@2-3" apart with 1/16" holes. The root growth is the same
as the cables with this set up.
     The CO2 injection works also very well. I like to control my
"reaction" a bit more than this approach offers and bubbles coming out
of the gravel  didn't appeal to me .Also pockets of gas would "burp"
every so often. I like to use DIY yeast for CO2 and this didn't offer
the control I needed. Cylinders ,were you can dose the rate in a more
flexiable manner, would be more desirable for this method. CO2 is so
important to the high light tanks that I tend to dedicate a separate
system and leave the subsrtate out of the system loop.
      Hope some of this helps out.
   Tom Barr     AGA