Brief Review

There are a couple of DIY methods to create CO₂ for your aquarium, each one with its own pros and cons:

1. Baking Soda + Vinegar
   The fastest, easiest and cheapest way to create CO₂. However, it doesn't last long. Thus requiring constant intervention to keep the CO₂ production.

2. Yeast + Sugar
   A little more complicated then the previous one, but still easy. The production last for some days, but is somewhat irregular. After some days, acid starts to buildup, which kills the yeast and stops the CO₂ production.

3. Yeast + Sugar + Baking Soda
   The baking soda neutralizes the buildup of acid and increases the CO₂ production. After some fine tuning, this method can last for 1-2 weeks and will only stop after the yeast have consumed all the sugar. However, the CO₂ production is still somewhat irregular (a peak in the first few days followed by a fast decay).

4. Yeast + Sugar + Baking Soda + Gelatin
   The goal of the gelatin is to control the sugar consumption. It takes some trial and error to fine tune the proportions of the ingredients. You will notice that different manufacturers requires different proportions. However, after doing so, this is the method that can last longer (up to a month) with the steadiest CO₂ production.

   

This article will discuss solely the 4th method for CO₂ production. The delivery system into the aquarium and other production methods will be discussed in other articles.

First part: Gelatin

Materials Required

• 1 PET bottle of 2L (Coca-Cola, Sprite, 7Up, Mineral Water, …) well washed.
• 4 packets of common gelatin (any flavor).
• 1 cup of sugar, ±200gr.
• 1 teaspoon of baking soda.

Steps

1. Prepare the gelatin according to the package instructions and, while still warm, add the cup of sugar and teaspoon of baking soda to dissolve.
2. Put the mixture in the bottle and leave it in the refrigerator until the gelatin hardens. Do not use all the space available in the bottle. Leave enough space in the top area in order to add the second part of the recipe.
3. Once the gelatin has harden, remove it from the refrigerator and leave it at room temperature.

Alternative
Some folks prefer a softer gelatin instead of hardened. That's up to each one taste, there is no right or wrong answer.
The tradeoff to care about here is very simple:

• Softer gelatin means the sugar will be consumed faster, therefore there will be a more pronounced peak in the CO₂ production.
• Harden gelatin means a more steady CO₂ production.

Second part: Fermentation

Materials Required

• 1 teaspoon of dehydrated organic yeast (sachet).
• 1 teaspoon of baking soda.
• 1 cup of sugar.
• 1L of warm water.

Steps

1. Dissolve the organic yeast and baking soda in a small amount of warm water. Put it inside the bottle and watch the level. There should be a free space at the top in order to contain the foam that will form, about 10cm is great.
2. Complete the bottle with warm water and screw the cap. The production starts in no time.

Attention

• Warm means really warm. If it is hot instead, the yeast will be killed and goodbye recipe.
• This mixture generates foam. Therefore you should never fill the bottle completely, otherwise there is a risk of such mixture getting into the aquarium.
• If you don't let the CO₂ get out, the pressure will increase inside the bottle which can ultimately explode !!!

Budget Issues

Colorless gelatin sold in sheets is much more expensive than ready-made gelatin, for example:

• 1 sheet of colorless gelatin = $3.90
• 4 boxes of ready-made gelatin = $2.60

Also, colorless gelatin requires more sugar while the ready-one has already half the sugar needed.

Therefore, there is no reason (besides esthetics) to use colorless gelatin in this DIY.

Further Reading

• Freshwater Aquarium: Beginner's Guide
• Freshwater Aquarium: Beginner's FAQ