CO2 Pads "Green Pads" explained - DIY Project NOT with smelly yeast.

Anyone try these things out yet? I am curious, and would like to try them in my small 8 sqft tent. Anyone?

CO2 Generation - another effective cheap crude method that could be refined by drip action

CaCO_3(s) + 2 HCl_(aq) → CaCl_2(aq) + CO_2(g) + H₂O_(l)

in other words,

Calcium Carbonate solid + Hydrocholoric Acid liquid = Calcium chloride + Carbon Dioxide gas + water

Where do you get Hydrochloric Acid? Lowes in the solvents section of the paint department ($8-9 for plenty). Often it is call Muaratic Acid and packaged in a plastic bottle. As with any acids, care must be given as it will burn you and ruin clothes, but with simple and careful planning / handling, hydrochloric acid should be easy enough to work with. Common sense and slow deliberate actions.

Where do you get calcium carbonate? many places including Lowes. Naturally, many things are made from it to include sea shells, coral, egg shells, snail shells. An easier source is from Limestone or better yet, marble (limestone that has been extremely heated and pressurized inside the earth). You can buy 40 lbs bags of quarter size rocks at Lowes in the garden area for < $5.

How can you use it? Simple put the marble rocks in a plastic container, add some water, pour in the hydrochloric acid. You get 8-12 hours of carbon dioxide production.

A simple set up would be: attach some hose to the bottle top of a wide mouth bottle (like a 3 liter) and run the hose to your plants (or fan for dispersion). Drop 5-6 decent rocks in there, fill the container 1/4 full of water, pour in an once or 2 of acid and put the bottle top/hose back on. Depending on your aeration in your grow room, you may either add more acid or more lime stone as necessary.

Caveats:
1. stuff a bit of polyester cloth in the tube near the bottle cap so residue / fizz mist cant go into and travel through your tube.
2. I tried limestone I picked up from nature and it contains other things like clay and other minerals that eventually form a mud layer over the rocks thus not allowing the acid to effectively make contact or the contaminant itself would bond with the acid and inhibit CO2 formation. Marble works the best.
3. You can use baking soda instead of marble. Many people use vinegar and baking soda, but vinegar is a 'weak acid' while hydrochloric acid is a 'strong acid'. Hydrochloric acid gives you much more bang for your $/buck. Much more.
4. Once the reaction stops the mixture will have either more marble left or more hydrochloric acid left to react with. It is safer to 'top off' by adding marble rocks and a little water than to just add more acid. i always ensure the mixture's acid is depleted before I add more acid. See #5 for why.
5a. you can continue to add rocks and acid to the container till the mixture is saturated with contaminant and calcium chloride. I then add a cup of water and some more marble to make sure there is no more acid to react with. I dispose of the mixture by pouring it onto on to a pile of lime normally used to adjust ph of soil or lawns (or onto a tree stump I am wanting to ensure is dead). Though the mixture is 'toxic' as is, it will neutralize and break down. It is unlike many pollutants that won't and remain persistent. It will effect ph of surrounding soil for some time.

5b. I recently used a bottle of 'low odor' hydrochloric acid and it seemed to not work as well with marble but did just fine with baking soda. A better explanation is that after the first 5-6 rocks in that container, I added more rocks (to see if any acid was left to react with) and saw very little action - it only partially dissolved the marble by the next day. When I put a spoonful of baking soda in that same rock/acid mixture, the baking soda reacted and it took 4-5 spoonfulls to deplete the remaining hydrochloric acid in the mixture. I poured that all out and tried again with with a new solution of 5-6 rocks - normal reaction for several hours. I put more rocks in the next day and little reaction. I squirted in some off-the-shelf hydrogen peroxide (H2O2) and the reaction started taking place again with the newer rocks and remnants of the old rocks. It seems the 'low odor' kind gets saturated very easily and the weak peroxide basically diluted the saturated solution to below saturation point. The peroxide easily would break down in the mixture and provide even more. I can also assume some o2 (oxygen) was also made.

Though this CO2 method sounds rough and crude, it is not hard to do and could be easily refined and made more precise. I don't see the need since my air is exhausted and I know I am loosing CO2 with the exhaust. I don't have the want nor the funds to measure CO2 levels. For me, just raising the CO2 in the less accurate way I do has dramatically improved growth. Good enough for me right now.

some thing else about CO2: It is heavier than oxygen and it lowers pH of liquids. It sinks to the bottom of the grow room so you must have decent circulation to make the best use of it. My air pumps were on the grow room floor and therefor picking up and pushing CO2 into the hydroponic nutrient solution. My pH started to drop when I started making CO2. I moved the air pumps and the pH drop problem went away.

This may not be the clearest post, but the basics should be easy and a method to make CO2 like this can be refined very easily.

Where to get a metered dripper?