Just thinking.. wouldn't most plants in nature grow outwards to the sun and reach the surface where co2 would be readily available. The plants aquarists keep must be trimmed and submerged, and therefore require co2 injected into the water column. I might be way off, just guessing.

My plants were growing pretty well without high lighting or CO2. I recently upgraded my lighting from about .5 WPG to nearly 3 WPG and I have seen a difference. The plants were getting streched out under the low-light and since adding the higher lighting, they are growing new leaves near the bottom of the stalks like crazy. I also set up a simple DIY CO2 system last week to test it out. I simply made a mixture of Yeast, Sugar, and Water in a 2L soda bottle. A hole was cut in the cap to allow the airline tubing to set about 1 inch into the bottle. I used silicon sealant to seal and hold the tubing and put a no-return valve in the middle of the tubing so the water from the tank can't return to the bottle and cause a syphoning overflow mess and destroy my tank! I put the other end in the intake of my HOB filter so the impeller can dissolve the CO2 bubbles and return them to the tank. It began bubbling about 1 hour later and has been going strong for about 5 days now. I have been monitoring the PH and it is holding steady at 7. I guess time will tell if the CO2 is really benefitting the plants.

Yeah, I am monitoring the PH as an indicator. I read up on this a bit and the main indicators are the PH getting too low and the fish gulping for air. We run our bubble wand every once in a while to keep O2 levels up (not sure if it actually does anything, but looks cool). Out fish have been just as active as the day I added the system, so it doesn't seem to be a problem. Other indicators have also remained steady. One thing I should have done that people recommend, but isn't probably necessary, is to add a second smaller bottle between the CO2 chamber and the tank so any backwater from the tank or gunk from the mixture is trapped. There is an awesome how to at the following link regarding DIY CO2.

http://www.fishforever.co.uk/carbondioxide.html

I put 2 cups sugar into a 2L bottle and filled it to the top of the label with warm water. Shake this around to dissolve the sugar. I then added about 1 tsp of Dry Active Yeast. The amount of yeast is a great way to monitor CO2 also. As I used the higher end of the spectrum, it is producing more CO2 at a faster rate. Recommendations are between 1/2 to 1 tsp. I will probably add less in my next mixture. Also, the no-return valve was a check-valve. I couldn't think of the name last time.

I am sure that your question has been answerred, however i use eco-complete, as well as a small amount of white sand just for a little bit of a salt and pepper look, only on one side of my tank it's pretty neat and is also quite effective, my plants have never been better looking, the eco-complete is perfect. no need for the sand other than the look i was going for.

Hope this helps.
Brandon

LOL peter am uploading them today, you will be the first to know when i have em on here. i'll send ya the links. :-)
Brandon