Alternatives to High-Tech CO2

Not ready to take the plunge? These alternatives can still attain great plant growth.

A high-tech, pressurized CO2 system is costly, and can be a headache to set up and maintain, especially if you’re just getting into the hobby. If you’re eager to start your first planted tank but aren’t quite ready to take the plunge on a high-tech setup, there are a few alternatives that can also achieve good results if implemented effectively.

Why supplement CO2?
As we discuss in our low-tech setup guide, plants require CO2 as a carbon source to grow. In nature, most aquarium plant species do not grow fully submerged, so are able to take in CO2 from the air, which has a much higher CO2 content than the water. Therefore, for plants to grow fully submerged in our home aquariums, it is ideal to supplement additional CO2.

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DIY CO2 Systems
There are a few options for low-tech CO2. We discuss how to build a yeast reactor, which generates CO2 through yeast fermentation of sugar. These systems are easy to build, maintain and are the most popular form of DIY CO2.

There are a few other alternatives, for example, DIY kits that use baking soda and vinegar. However, CO2 generated by these kits may be somewhat difficult to control and increase risk of overdose, so we’d recommend sticking with the yeast if you’re going the DIY route.

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A DIY CO2 system is best-suited to smaller tanks of less than 30 gallons. For larger tanks, it may be possible to build more than one reactor, but the trouble here is that you not only need to produce CO2 but also to efficiently diffuse it, which may not be feasible for more gallonage.

Flourish Excel
Seachem Flourish Excel is a liquid supplement added to the water, which is a bioavailable source of organic carbon for aquarium plants. Aquarists report that consistent dosing with Excel doesn’t achieve quite the results of a pressurized CO2 system, but does make for noticeable improvements to plant growth. Another benefit of Excel is that it’s also an algaecide, so helps prevent algae blooms.

Downsides to Excel are that it must be dosed daily or every other day to achieve optimal results, and even slight overdosing can be toxic to livestock, especially invertebrates. If purchased in bulk Excel is relatively affordable, but it is an ongoing cost rather than an up-front investment, as with a CO2 system.

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Low-tech non-CO2 setups
As we cover in our low-tech setup guide, it is possible to maintain a planted tank without supplementing CO2, although plant growth will be slower. The key here is to choose low-maintenance plant species and balance your lighting and fertilization accordingly.

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Tailoring your planting, lighting, and fertilization
These systems will not be as efficient as a high-tech setup, so you may want to stick with less-demanding plant species such as stem plants, crypts, java ferns, anubias, and mosses. Some species of sword plants, such as Amazon swords, may be compatible, but will not grow as large or as robustly as in a high-tech setup.

Also, keep in mind that your plants will not be photosynthesizing as efficiently as with a high-tech CO2 system, so you will need to adjust lighting accordingly. Keep lighting under 2 watts per gallon.

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To fertilize a tank supplemented with low-tech CO2, you will need to test nitrogen, phosphorous and potassium levels consistently to get a feel for what your plants’ nutrient needs are. We’d recommend starting out with the following guidelines intended for non-CO2 tanks, and increase gradually from there in the case of DIY CO2 and Flourish Excel tanks. Per 20 gallons, dose weekly:
  • 1/4 Teaspoon Seachem Equilibrium
  • 1/8 Teaspoon Potassium Nitrate (KNO3)
  • 1/32 Teaspoon Potassium Monophosphate (KH2PO4)
See our article for more information regarding Estimative Index (EI) dosing, but keep in mind that some of the numerical guidelines given here are for high-light, CO2-supplemented tanks.

Because you want to be wary of overdosing macronutrients in these setups, we’d also recommend against soil-type substrates, which contain macronutrients, so could result in imbalances in a low-tech system.

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