Cheapest, easiest, safest, most reliable, most down low CO2 generator
I think that this type of CO2 generator is sometiems called a "fizz pot" - it is, a bubbling vat of acid, water, and calcium carbonate. This is a very good co2 generator for a medium sized grow room (the room I use is about 1000 cubic feet in volume - 8 feet by 8 feet by 14 feet).
Set-up (cost):
-a common plastic five gallon bucket ($2.79)
- hydrochloric acid (called "Muriatic Acid"; 30% hydrochloric acid costs $8 for two gallons -7.5 liters - at swimming pool supply houses; Home Depot - and Safeway also - sells 14.5% hydrochloric acid @ 2 gallons for $8)
- bag of marble landscaping chips (calcium carbonate - CaCO3: $8 for a 30 pound bag at Home Depot).
- water
- an old cotton towel
- a wooden board about 16"x12"
- an old coffee pot (or large dipper - 2 quarts or more is best)
This is the chemical equation that occurs: CaCO3(s) + 2 HCl(aq)=> CaCl2(aq) + CO2(g) + H2O(l).
The hydrochloric acid dissolves the marble chips to produce CO2 and calcium chloride (much like table salt - it is not toxic but I do not recommend eating it)
1. Put a layer of marble chips in the bottom of the 5 gallon bucket.
2. Fill the bucket with water to within four inches of the rim
3. depending on the size of the grow room, EACH DAY add a CORRECT AMOUNT (see below) of Muriatic Acid
4. you will see the acid react with the marble chips to start producing co2; it starts bubbling away merrily as the acid dissolves the marble and creates co2, calcium chloride (salt) and water.
5. cover the bucket with the board, then cover the whole thing with the towel (the towel is to filter out mineral oil that occurs naturally in marble chips - see below; the board is to keep the towel from drooping into the acid/water mix - no big deal except that the acid will eventually dissolve the towel)
6. the reaction produces very salty water (calcium chloride is used for ice control on roads in the U.S.); otherwise, it is completely safe
The co2 generator can be controlled with great precision! Using the correct amount of acid allows you to save money. It is worth the trouble to take 5 minutes to understand the chemistry of the reaction - specifically, the wise grower should learn how to correctly calculate the CORRECT AMOUNT of hydrochloric acid to add each day.
Let's talk stochiometry (the science of getting stoked ... well, uh, actually stochiometry is the science of measuring chemical reactions.
First of all, you need to get your mind around the quantitative concept of a "MOLE" (a "molecular weight")
A "mole" is a specific quantity of any substance; specifically, a mole is: "6.02214179 times 10 to the 23rd power" ... blah blah blah ... In stoner talk that is 602,210,000,000,000,000,000,000 molecules of calcium carbonate all piled up in one place okay?
Conveniently, ONE MOLE of calcium carbonate WEIGHSs almost exactly 100 GRAMS.
One mole of water weighs 18 grams. One mole of hydrochloric acid weighs ... who cares, you are never going to weigh any HCL
One mole of co2 weighs 44 grams. You need to understand that, once 100 grams of calcium carbonate has been converted into calcium chloride, co2, and water, the mole (44 grams) of co2 that bubbles up is 24.5 liters of co2 gas (Boyle's law at 25°C and 1 atmosphere pressure). I REPEAT: 100 GRAMS OF MARBLE CHIPS WILL PRODUCE 24.5 LITERS OF CO2 (28 liters = approx. ONE CUBIC FOOT).
See how beautiful this equation is??? 115 grams of marble chips will interact with the hydrochloric acid to produce almost exactly one cubic foot of pure co2.
One cubic foot of co2 will enrich my 8'x8'x14' grow room by precisely 1000 ppm (if the room is sealed air tight which never happens - see below).
To correctly calculate the presice amount of hydrochloric acid to use, note that:
30% HCL swimming pool acid = 9 moles of HCL per liter (about 32 moles per gallon); 14.5% HCL swimming pool acid contains 4.5 moles per liter (about 15 moles per gallon).
Note that the chemical reaction (CaCO3(s) + 2 HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)) requires two moles of HCL for every one mole of calcium carbonate (to produce one mole of co2).
So then, for my 1000 cubic foot grow room, with several pounds of marble chips sitting at the bottom of five gallons of water, I will add (crudely measured) about quarter of a liter (about two moles) of 30% swimming pool acid.
SAFETY, BY-PRODUCTS, AND DISPOSAL OF THE SALT:
NEVER POUR WATER INTO PURE ACID. ALWAYS POUR THE ACID INTO THE WATER. THAT WAY IF ANYTHING SPLASHES OUT OF THE BUCKET, YOU DO NOT RISK GETTING AN ACID BURN. But don't let the word "acid" freak you out - even 29% HCl it is not especially dangerous. I do not recommend pouring acid on yourself, but even if you get pure 29% acid on you, it won't eat a hole thru your skin and muscle and corrode your bones. Actually, I don't even worry about it any more - I just wipe off anything that splashes on me and don't even notice it. Even so, a splash-out or an HCL spill is definitely to be avoided - keep a couple boxes of baking soda around to neutralize acid spills just in case. Small acid spills are somewhat unavoidable so I repeat: keep some crushed up TUMS antacid or a box of baking soda around to quickly neutralize acid spills.
Marble is limestone that has been compressed by geologic forces. You can also use marble flooring tiles which are much purer CaCO3 (but at Home Depot, they are 2x the cost as landscaping chips).
DO NOT USE RAW OR NATURALLY OCCURRING LIMESTONE - it stinks. Although limestone is almost pure calcium carbonate, country rock limestone often contains tiny quantities of sulfur dioxide and mud; it will make the gro room smell like rotten eggs, and, as the limestone dissolves, the mud particles soon created a mud shield that prevents the acid from reaching the limestone.
Broken chunks of common concrete work very well: they are free and contain very pure CaCO3. The problem with broken concrete is the weight - most common concrete contains only about 10%-15% calcium carbonate cement. ONe advantage to broken up concrete chunks is that the high quantities of sand and gravel in the concrete buffer (slow down) the reaction very nicely (thereby reducing the problem of leakage of highly concentrated CO2 out of the grow room. I have ofen thought about buying a 60 pound sack of pure CaCO# cement at home depot, mixing it up, and pouring it into 5,000 old egg cartons to produce a lifetimes' worth of handy, bite-sized pure cement CaCO3 chunks, but ... idk ...
COVERING THE FIZZ POT WITH THE TOWEL AND THE BOARD IS IMPORTANT! Marble contains naturally occurring mineral oil - the towel will filter out the vaporized mineral oil quite nicely. If you do not use the towel, after a couple weekS you will get a thin layer of mineral oil all over everything in the grow room - including the buds of your marijuana plants. It doesn't hurt them, but it doesn't help either.
Perhaps the biggest drawback to this system is that it produces alot of calcium chloride salt. Note that one mole of CaCO3 produces one mole of calcium chloride (CaCl2) salt (i.e. every day you will be generating about a quarter pound of salty salt). The CaCl2 remains dissolved in the water in the bucket - it does not get airborne. CaCL is super salty stuff - they use it up north on icey roads. Modern societies generate hundreds of thousands tons of salt waster every year and all municipal sewage treatment facilities are specifically built to treat and remove salt waste. Soo, just keep paying those utility bills and your taxes and you can feel good about safely pouring the CaCO3 water down the drain, or you can use it to kill weeds in the alley behind your house like I do.
Every week or so, it is wise to use the old coffee pot as a dipper to help you empty out the salt saturated water in the bucket. Do not try to pick up and carry the bucket - it has marble chips and heavy salt saturated water in it! Use the dipper to empty it a little at a time.
The marble chips they sell at home depot are not pure marble - there are other kinds of minerals in there too. After 2-3 weeks, you will notice that instead of just the pure white marble chips, there is also funny colored gravel in the bottom of your bucket. Don't worry about it - every month or so just dump out the gravel and replace with fresh marble chips. Using marble floor tiles (each tile weighs 7 pounds- it is pure marble - floor tiles cost about $3 each at Home Depot- also, by calculating the surface area of the broken up floor tile, you can very accurately calculate the exact weight of CaCO3 if you so desire; an Extra Strength TUMS = .5 gram pure CaCO3 for microgrowers).
The five gallons of water is called a "buffer" - it slows down the reaction quite handily. The colder the water the better to slow down the reaction. 90% of the hydrochloric acid will be used up in the first hour (thus quickly enriching the grow room) then, as the dilute acid solution continues to dissolve the marble chips, the co2 fizz pot continues to add minute amounts of co2 as the plants use it up.
Keep a small fan in the gro room to constantly stir up the air. CO2 is heavier than air and will quickly settle to the bottom of the grow room beneath where the plants can use it. Without a small fan to stir up the air, even ten cubic feet of CO2 would settle to the floor and uselessly form a layer of CO2 a few millimeters thick.
Consider the costs per day to generate :
115 grams of marble chips = about 8 cents
two moles of HCL = about 25 cents
It is soooooo easy: every day when the lights come on just dump some acid into the fizz pot, and close the door - no need to come back and replenish anything. Every week or so, check to make sure there is enough marble in the bottom of the bucket and change the water.
CO2 DISSIPATION OUT OF THE GRO ROOM: in my gro room, even though one cubic foot of co2 is all I need, I actually use twice as much as I have described. This is because my grow room is not well sealed - the warm hps lights heat the air which rises thru the ceiling and then to the top of the boathouse and leaks out through the gaps where the roof meets the walls. - the warm air carries co2 with it. Therefore co2 unavoidable leaks out for the whole time the lights are on. But who cares?? Several internet sources report that MJ plants thrive at co2 levels 700 ppm - 2000 ppm. By running up the co2 to 2500 ppm at the beginning of the light cycle, I can count on natural leakage to reduce it down to usable levels pretty quickly. (CO2 > 10,000 ppm is toxic to plants). Using twice as much CO2 as I need from the beginning does not seem to have ever hurt anything - to the contrary, it is amazing how much it helps! Especailly in vegatative phase for photoperiod plants.
I used to use a much smaller system in a 4'x2'x2' stealth microgrow. To generate tiny quantities of co2, use the plastic jugs that the Muriatic Acid came in, and carefully measure out the right concentration of hydrochloric acid and water. To enrich a 16 cubic foot grow space, I need only about half a liter of co2; about two grams of marble (.02 moles) and only about two table spoons (2/3 oz) of HCL was sufficient.
Consider all the benefits of this co2 fizz pot system:
- it's cheap
- there is no compressed air tank to leak and drown the downstairs neighbors or pets in co2
- there is no compressed air tank to arouse the paranoia of the neighbors
- everything is available locally
- the reaction can be controlled very precisely by regulating either the weight of marble or volume of acid
- it can be disassembled instantly (in case it needs to be hidden in a hurry)
- in a pinch - for example if the poli are pounding on the front door and saying they have a search warrant - the fast thinking grower could stuff all the plants into the bucket and pour the hydrocholric acid over them, thus destroying the evidence (making it untestable)
I was able to keep my grow room hidden from my wife for several months by telling her, "Do not go in the boathouse. I am using carbon dioxide to kill termites in there" (finally she figured out where I was growing all the pot I was smoking)
