Hands On: DIY CO2 Generator

co2 generator

Just in case you’re wondering, I frequently partake in the deals I post on this site.  I picked up the Aquarium DIY CO2 Generator from BangGood a while back.  The interesting thing about this setup is that it uses citric acid and baking soda in two bottles to generate CO2 for the aquarium.

co2-generatorNow that I’ve had some time to play with this toy, I thought I’d share my impressions and maybe add some more information on using this method for CO2 generation since there’s not a ton of information out there about using citric acid and baking soda instead of  yeast to create a CO2 reaction.

This setup adds a pressure gauge, plus an emergency release valve along with a needle valve to control the output of CO2 from the generator.  You bring your own two liter soda bottles plus additives to complete the thing.  Consider it semi-DIY if you prefer.

The basic idea is that you put citric acid (more on this later) with water in one bottle and baking soda and water in another.  Squeeze the bottle to begin siphoning citric acid water into the baking soda bottle and a reaction begins to produce CO2 gas which is then sent through the needle valve and out to your planted aquarium.

There are a couple of different versions of the product.  The one I’ve been using and is pictured in this review is the D-501 model.  This model has a rigid bridge between the two bottles that makes everything an easily-contained single unit.  There’s also a model 301 that features the same gauges but attaches via individual specialized bottle caps and might offer some more flexibility for placement in the bottles.

A D-201 model also exists, but it seems like the components are much more cheaply made than those in the other two.  There’s only a couple bucks difference between that one and the 301 and 501, so I’d just skip the 201.

Did I mention all of these units are under 20 bucks each?  That would explain what it’s doing on this blog.


I sprung for the extra 3 dollars to ship my CO2 generator express. That option got me my product within 3 days via DHL.  Well worth the price since normal free shipping takes up to 3 weeks.

co2-generator-chinese-directionsSadly, the pressure gauge broke off my unit shortly after getting it.  Customer service had me e-mail them a picture of the broken piece and then happily sent me a replacement. No complaints there.

Once I got a working unit in hand, it was time to begin the great experiment.  The instructions that ship with this product are in Chinese, so that’s not exactly helpful.  Fortunately, the product description on BangGood’s site has an English translation.

Even more helpful is this article you’re reading right now where I can explain everything in plain English.

To begin  you’ll need two 2-liter soda bottles.  Use soda bottles, not juice or punch as soda bottles can handle much more pressure.  When you’re done with the setup there will be quite a bit of pressure held in these bottles.

I’ll be referring to the DIY CO2 Generator in terms of left and right.  Looking directly at the unit, the side with the pressure gauge will be the left, the needle valve on the right.

After you’ve enjoyed your beverage of choice, rinse the bottles out well.  It doesn’t have to be perfect as only the gas is going into your fish tank, not the liquid (unless something VERY bad happens.)

Begin by closing the needle valve on the right side.  Don’t go all crazy tightening it, or it’ll be a pain to loosen when the time comes.

Start with the citric acid bottle (the one on the left). You’ll want to keep these straight, I labelled each one with a Sharpie. Get out your trusty funnel and add 7 oz (200g) of citric acid powder. Then add about 20oz of water to the bottle.

A note about citric acid: you can find this stuff in the canning section of your grocery or discount store. It’s typically used in canning tomatoes.  It’s also pretty expensive in that form.  My store has 5oz bottles for about 4 dollars.  A much better alternative is to hit up eBay.  I bought a 5lb bag of the stuff for less than $15.

Setting-up-citric-acid-baking-soda-co2At this point, shake up the bottle and screw the bottle into the left side of the generator, under the pressure gauge. Then fill the baking soda bottle with 7oz of baking soda and about 7oz of water. Shake and attach that one to the CO2 unit on the valve side.

Now the magic begins.  Squeeze the citric acid bottle firmly until you can’t squeeze any longer. Unless you’re the Hulk or something, don’t break the bottle.

When you release the bottle, citric acid solution will siphon into the baking soda side.  If you remember your school science fair, this is the same thing that happens when you make the volcano with vinegar and baking soda.

Next, open the needle valve wide open for about 5 seconds and then close it again.  Then repeat the squeeze and valve open again.

The idea behind this is that the pressure differences in the two bottles will cause the citric acid to siphon into the baking soda bottle until an equilibrium is achieved. Once that happens, the system will siphon citric acid as needed when the pressure drops.

You want to continue this process until the gauge reads around 2kg of pressure.  This can sometimes can take some patience.

If you’re like me and not patient, after you do the valve thing a time or two, give up in frustration and give the assembly a gentle shake.  This tends to speed up the reaction and builds pressure more quickly.

Don’t shake too hard, the system is setup with a pressure release valve that will open up if too much pressure builds up. That’s great for safety, but it kind of wastes your CO2.

Don’t sweat the pressure too much.  Once you get the system up to around 1kg of pressure, it’ll pretty much get to the right level in use.

Once you have the reaction going, hook the needle valve up to your air hose (use silicone or specially designed CO2 hose).  Hopefully you remembered to buy an air tube and some kind of CO2 diffuser or reactor when you ordered this thing. I’ll put a list of stuff to get for the full CO2 setup at the end of this article.

Hook all that stuff up and then open up the valve to get the CO2 goodness flowing.  I tend to open it up a little wide at first to clear the tubing and then dial it back down to the desired bubbles per second in the bubble counter.

CO2 Generator in Action

Ok, so once everything was dialed in and hooked up I ran through a couple of cycles to get a feel for everything.  Unlike yeast-based CO2 DIY setups, there’s no problems with pressure.  While it might not pack as much pressure as a proper pressurized CO2 setup, there’s more than enough force to make a nice stream of micro bubbles from a standard glass diffuser.

citric-acid-baking-soda-diy-co2-generator-in-useConsistency on the other hand is a little bit different.  I found that during the course of the day the flow of CO2 would decrease, requiring me to open the valve a little further in the evenings.  To be honest, I’m not sure if this is a flaw in the needle valve or in the CO2 generation process itself.

According the the manufacturer, using the system 8 hours per day, you can get over a month of use running at 1 bubble per second (bps). A rate of 3bps is only good for about 20 days.  My photo period is longer than 8 hours, so I tended to get a little under two weeks at 2-3bps.  That’s where the eBay citric acid comes in handy.

Basically, in my opinion, this system sits between a yeast-based DIY system and a proper pressurized CO2 system.  Performance is much more consistent than yeast, and more importantly, the output is controllable.  You also don’t need to wait a day or so for the CO2 to build up in this system since it’s a chemical and not a biological reaction.

Yeast systems may last longer between charges, but they’re just kind of hit and miss.  Of course a CO2 tank system is very consistent and lasts for months depending on your tank size.  Those systems also cost a whole lot more than this setup.

Ultimately, if you want decent performance and aren’t quite ready to commit to a dedicated pressurized CO2 system, using a citric acid and baking soda CO2 system is a very good compromise.

As promised, here’s a list of gear you want to pick up to have a fully functioning DIY citric acid and baking soda CO2 system. All items are from BangGood because they’re inexpensive and you can get everything in the same place. There’s other options too, so look around.