Red Sea Plant Lab Iron/CO2 Kit

Plant lab for the maintenance of correct levels CO2 & Iron for healthy plant growth.

Introduction to Carbon Dioxide 

For plants to grow, they form carbohydrates (sugars) out of carbon dioxide (CO2) and water, using light as the energy source. This process is called photosynthesis. 

In an aquarium fish and bacteria produce CO2 continuously. While plants use CO2 and have a net production of oxygen during the day, at night this process is reversed and they use oxygen and produce CO2. 

In a well-planted aquarium the amount of CO2 that is produced naturally is relatively small and therefore the CO2 concentration is usually the most dominant factor limiting plant growth. 


CO2 Equilibrium 

CO2 gas dissolved in water can take the form of bicarbonate or carbonate. These three forms are in chemical equilibrium. Which form is present in what amount depends on the pH. 

Dissolved CO2 <=> bicarbonate ion <=> carbonate ion 


In the pH range favorable to water plants, pH 6.4-7.2, a percentage will be present as dissolved CO2 and the rest as bicarbonate ions. 


From pH 8.0 to pH 8.8 there will be almost no dissolved CO2, a large amount of bicarbonate and a small amount of carbonate. 


Although they are named "water plants", most aquarium plants are really swamp plants that grow in their natural habitat with at least part of their leaves above the water line. Therefore, they have adapted to take up gaseous CO2 from the atmosphere. In the aquarium, placed under water, they are only able to use dissolved CO2. Several real water plants, meaning species, which are always under water in their natural habitat, are capable of also using the bicarbonate ion if CO2 availability is limited. It is not however favorable to allow this to happen, firstly because many other plants in the aquarium will be unable to grow. Secondly, with the use of bicarbonate ions the pH will rise to unacceptable levels for all plants. 


Because of the CO2 equilibrium discussed, the maximum amount of dissolved CO2 present is dependent on the pH. The lower the pH the more CO2 present. 

Since plants use CO2 in considerable amounts, they increase the pH at the same time. Thus the pH value and the CO2 concentration are interrelated. 


Carbonate harness (KH), is yet another factor that effects the concentration of CO2. Hard water, with a high KH can hold more CO2 than soft water. While it is essentially true that hard water with a low pH holds the largest amount of CO2 in practice we can only use the values most suitable for plants, which are pH 6.4-7.2 and 3-8o KH. 


The water plant enthusiast faces the task of maintaining both a stable pH and hardness in order to establish an optimum CO2 concentration. 


Summary and conclusions 

Most water plants can only use dissolved CO2 and are therefore incapable of taking up bicarbonate. 
The Maximum amount of dissolved CO2 present depends on the pH and the KH. 
Plants lower the CO2 concentration in daylight and thereby increase the pH. 
Values of pH 6.4-7.2 and 3-8o KH should be maintained for optimum results. 
To maintain optimum plant growth results, regular CO2 tests together with the pH and KH are required. 
Introduction to aquatic plant growth 

Healthy plant growth in an aquarium is dependent on the following: 

Light and CO2: Essential components in the photosynthesis process. 

Oxygen: At night plants use oxygen and produce CO2. 

Temperature: Most aquarium plants are tropical and therefore require a water temperature of 73-80°F (23-27°C). 

pH: An optimal pH value must be maintained to ensure peak growth levels. 

Water Circulation: Moderate water circulation supplies the plants with dissolved nutrients and removes waste products. 

Minerals: Aquarium plants require many elements for healthy growth. 

The following major elements are essential: Nitrogen (N), Phosphorus (P), Calcium (Ca), Magnesium (Mg), Potassium (K), Iron (Fe), Sulfur (S). 

Although trace elements, such as Molybdenum (Mo) and Manganese (Mn), are only required in minute quantities, deficiency in one of these elements will have an adverse effect on plant growth. 


More than sufficient amounts of Nitrogen and Phosphorus are usually present in the aquarium on account of the introduction of Nitrate and Phosphate during the feeding process. Although these compounds are essential to plants, a surplus can lead to growth stagnation and development of algae. It is therefore recommended to regularly test the nitrate and phosphate level, (using Red Sea`s Nitrate & Phosphate Test Labs), and to keep the concentrations low by weekly 10-20% water changes. 

Calcium, Magnesium, Potassium and Sulfur (as sulfate) are usually sufficiently present in tapwater (a second reason to perform weekly water changes). 


Iron is a very important element that is required by aquarium plants for healthy growth.The Iron consists in sea and fresh waters as soluble and insoluble compounds. Insoluble compounds (oxides and hydroxides) are deposited at the bottom. The soluble iron compounds consist of truly soluble complexes of ferric iron, colloidal ferric hydroxide and phosphate particles. 

The uncomplexed ferric ion cannot exist in an amount of more than 0.1 ppm at pH values of 4 or more. 


The presence of the complexed (chelated) Iron is largely dependent by the presence of organic matter. Water plants can only consume dissolved iron from the water. Even when the substrate is very rich in iron oxides or other insoluble iron compounds, iron deficiency may still occur, since these compounds are unavailable to the plants. It is established that chelated Iron, (including EDTA-Iron complex), can only be taken up by plant roots. The leaves and stems do not have the ability to extract Iron from a chelate. 

Iron deficiency frequently occurs in planted aquariums. The symptoms are growth stagnation and yellowing of the leaves. 

By the regular monitoring of Iron concentration for some weeks you can determine the Iron requirement of your aquarium. 


Recommended Use of Iron Test 

The Iron Test should be performed weekly. It is advisable to write down the test results in a note book, so that any gradual decrease in the iron concentration will become apparent. 

Should your test indicate less than 0.1 ppm of iron, the concentration should be raised immediately, either by using a liquid iron additive or by fertilizing the aquarium bottom with an iron rich substrate such as Red Sea’s Flora Base or Flora Root. 

A downward trend of the iron concentration should be halted and stabilized by regularly using a good plant nutrient mix. A stable and favorable Iron level as well as a constant supply of essential trace elements is achieved by a daily addition of Red Sea’s Flora 24.