CO2 injection via wet/dry return

The subject of CO2 injected on the return side of a wet/dry is one
I have intimate knowledge of.  I use multiple tank setups with a large 
ENCLOSED wet/dry for both mechanical and biological filtration.
The reason for enclosed wet/dry filtration is to trap the ambient
CO2 as it is returned from other tanks in the system and reintroduce
it to the same tanks.  I inject to one tank and the CO2 seems to travel
to the others very well.  Keep in mind that the first tank will always
have the strongest concentration and therefore should have the lowest
fish load.  The combination of reoxygenation in the wet/dry area( although
my wet/drys are enclosed they still bring in air from the skimmers)as
well as continuous assimilation of CO2 from injection and re-
introduction of CO2 coming back from the other tanks keeps the oxygen
and CO2 at acceptable levels for fish health. It is alittle tricky
at first, but once it is balanced out it is ALMOST trouble free.

All plumbing parts are easily found at the local hardware.  The initial
expense of an enclosed wet/dry is soon outweighed by the resulting
plant growth.  It is extremely important to have the equipment on timers
so that the CO2 injection corresponds with the lighting.

I'd like to hear from others who have tried something similar and learn of
their successes and problems encountered.