i had a bit of a read of the no mercy site zandor posted.
i thought roots wanted oxygen not co2?
if they do thrive off a lil co2 should i put in another airstone and airpump which is pumping co2 from one of these diy units?

would be good to hear ur thoughts guys, this has really caught my eye
misk Reviewed by misk on . cheap and easy CO2 I read this in a school science site. To make cheap CO2 use vinegar and egg shells. Crush egg shells and put in a plastic container, then pour vinegar over egg shells. I took a one gallon water jug, drilled a 1/4 inch hole in the top and plugged one end of 1/8 inch black tubing. Then stuck holes along the tubing for the gas to escape. Hang tubing near the top of plants, since gas is heavy. Easy and cheap. Replace vinegar when mixture stops bubbling. Rating: 5