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Alrighty, Soooo all my tanks are planted, and i've realized there's been a few topics on CO2 injections..

My mate taught me this, it's cheap effective and... cheap.. :lol:


2L Bottle/ 1.5 L bottle... anything really.. any plastic juice bottle/coke bottle is good

2 Cups hot water

1 Cup Sugar (any, caster, brown, raw... not sure about icing sugar though..)

Length of air tubing

1 packet of dry yeast

CO2 Diffuser, or if you are really budget, a small air stone is good enough


1. Drill/cut/stab a hole in the lid of the bottle that is slightly smaller than the air tubing.

2. Feed airtube through the hole, so it sits about 2 inches below the cap, make sure the tube perfectly cylindrical when inside the lid (no folds/bends in the tube), otherwise there'll be a leak.

3. Attach diffuser or airstone to the otherside of the airtube.


4. Add 2 cups hot water to 1 cup sugar, make sure it's melted.

5. Fill the bottle to about half way, or just under with normal tap water, then add the sugar water

6. Sprinkle the packet of yeast into the bottle, you don't need to shake it

7. Lid on, put the diffuser into the water and.. in a few hours or less your c02 should be bubbling away!!

oh, and make sure you've got oxygen bubbling via filter or loads of plants or a bubbler or something, coz otherwise there could be an imbalance depending on the size of your tank..


The yeast will take around 2 weeks+ to run out of sugar to feed on, so to reactivate, melt another cup of sugar with a cup of hot water, then top it up with tap water to make it warm.. then just add that to the bottle...

You can probs do this twice before it gets icky... and really alcoholic/yeasty/vegemite smelling haha

Here's a pic to help you understand... it's pretty simple anyway



Oh, here's a diffuser on ebay


just search 'co2 diffuser' and a bunch of stuff should come up..

Edited by girlz0r
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hehe very cute picture you drew. in regards to the diffuser, make sure to get a nano diffuser if you have a nano tank as the normal sized ones will look really out of place! diy co2 should probably be used in tanks of up to 2ft... otherwise the bubbles usually do not make it much further and you'll have only a small portion of your tank receiving co2 before the bubbles reach the surface and not the plants.

most people doing diy co2 seems to put in 2 cups of sugar and half a measured teaspoon of yeast lasting usually 2 weeks - then they redo the entire mixture. another method you can use. also some people put in a pinch of bicarb soda as well no idea what this does...

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when you say too much co2 might cause an imbalance would it matter if the fish are only bettas since they take their oxygen from the surface not the water ?? or woudl it hurt their skin or something ?

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if you have a filter, as long as the filter outlet is agitating the water surface, there will be oxygen dissolved into the water. if the surface of the water is too calm then little oxygen will be dissolved. i don't use air stones as my filter is able to agitate the surface enough. the purpose of the airstone is to agitate the water surface more than it provides oxygen directly as the bubbles coming out of the airstones are usually too big so they float up and disappear before much of it gets dissolved into the water. if you have a hang on filter you should be getting enough oxygen. if you have a cannister filter make sure the outlet is positioned higher and agitating the surface. you will need an airstone if you have internal filters or no filters as there will be little to no surface agitation.

although bettas have a labyrinth organ, they still need dissolved oxygen in the water to survive. they cannot rely soley on one type of oxygen source.

i will also add.. co2 is really only needed for heavily planted tanks or high maintenance tanks - aka medium to hard plants (difficulty wise). easy plants can be kept in low tech tanks and will not need injected co2. do not feel that you need co2 in a planted tank. i have used liquid co2 for two of my smaller tanks and they are absolutely fine without co2.

Edited by Raie
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i see thankyou ! i will have to adjust my filter so it agitates the surface more. I added co2 because my plants where looking a little sick and my PH was really really high and i read adding co2 would lower it naturally?

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  • 1 month later...

I've read a lot on the 'net about DIY CO2, one of the points made frequently is that if you have a lot of agitation at the surface then there's not a lot of point with the CO2 as it will escape as quickly as you can get it into your tank. An air-stone in a tank with CO2 will cause way too much agitation and you will loose pretty much all of the CO2 before it can be utilized by the plants. A preferred method of injecting the CO2 into the tank is via the uptake tube of a canister filter, (if you're running one) the blades of the pump dissolve the CO2 quite nicely and it spreads through the tank with the current. I'm NO expert, just passing on what a LOT of articles have had to say.



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There is no point adding Co2 if you agitate the surface during the day. The Co2 will just gas off with the surface agitation. If you have adequate light, the plants will use the Co2 and give off oxygen, in which case, suffocation during the day is not a risk.

There IS a point to aerating at night, because the plants are respiring also then, and are releasing Co2 themselves. That is when your fish are at risk of suffocating. Assuming that your plants can use the Co2 during the day - as to which see my next point.

If you don't have enough/the right sort of light, there's no point adding Co2 at all, because the plants cant photosynthesise enough to make use of it. You risk your fish suffocating even during the day if your plants can't use the Co2 and convert it into oxygen.

Adding Co2 CAN drop the pH/hardness of the water, and can even cause a pH spiral, turning the acidity of the water to something akin to lemon juice. This kills fish and plants. You should have some sort of buffering item in the tank eg marble chips or shellgrit to buffer any acids in the water when using Co2.

As the above would suggest, I recommend research before people go adding Co2 to their tanks (no matter how cheap the manufacture is ;) ).

Also, DIY Co2 units are reknowned for exploding. Make sure your diffuser/air stone or whatever you use doesn't get clogged, or that lovely beer/yeast/vegemite liquid will go all over your walls.

Finally, it is not unheard of for these bottles to siphon out INTO YOUR TANK. This will kill everything. Make sure the bottle is kept BELOW the water level to prevent this happening - it won't siphon upward. I have never found a check-valve that actually works, so just don't risk it.

That's my 2c :)

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