CO2 diffusers vs. reactors

After listening to a lot of opinions, I've decided to stick with my
30-35% weekly water changes (at least until I get a python), but to add some
CO2 for my high-load 55 gallon (80watts). I made up a DIY CO2 system with
one 2L CO2 bottle in order to go slowly before adding a second CO2 bottle
(through a t-joint that currently has one arm sealed). I had problems with
the seal at first, but then just made a smaller hole on another cap, so I
now have plenty of CO2 coming into the tank through 1/4" silicon tubing.
In the short term I got an airstone (useless) and a clear plastic bell
to allow passive diffusion. This isn't working too well, as the CO2 builds
up and occasionally bubbles to the surface when the bell fills (the bell is
right beside my large HOB filter intake, I also have a second smaller HOB
filter on the other side of the tank). So my next step is to find a good
way of diffusing the CO2 into the water (I keep the water level high to
reduce surface agitation). I like the ease of diffusion compared to reactor
methods, especially since my wall plug is already bearing a heavy load! So
does anyone know of a good diffuser I could build or buy (in Canada)? I'm
looking at one from Big Al's:
http://www.bigalsonline.ca/catalog/p...3&pcid 1=3349

Does anyone have any experience with how efficient these style diffusers
are? Anyone know of good data on how efficient the various diffusion
methods are? I don't need ultra-high levels of CO2, but I haven't seen any
significant change in my pH or plant growth under my current (and admittedly
half-assed) set-up. As I said before, I prefer the diffusion method, but
I'm open to building/buying a reactor if that's truly a much better way of
going about it. I certainly don't see my current bell set-up doing much if
I add a second DIY bottle of CO2! Thanks,

Tony