Algae prevention part 1 - Plants biology

There is a lot of material on the web which treats about the algae prevention in one way or another. Anyone who own an aquarium has had this problem one or more times. Algae occurrence has made many of us stop their hobby forever. I decided to put on my blog all the information I could find and learn about this topic, both to organise my knowledge and to share it with anyone interested. This will be divided into several posts. First one is about plant biology, so what do we need to know to understand what is going on in aquarium.

When you start keeping aquarium as a hobby you will soon find out where the life as a whole began. All the life you see around you is only possible due to the smallest creatures you can find: bacteria. They were the first life forms, they made our atmosphere as it is right now and so on. Without them you would not have oxygen to breath. Yes, there would be no plants as we know them if not cyanobacteria known for aquarists more as blue-green algae. Yep, that one made the big oxygen crisis as they call it and wiped out most of the life present on earth from life beginning: anaerobic bacteria. That's the past. For any aquarist cyanobacteria is a big issue mostly due to the fact that it is not an algae but bacteria, what means that killing it may kill all the beneficial bacteria as well. Back to the topic. Bacteria is very important for aquarium and its inhabitants. You have all different types of them, I covered some in the post about the nitrogen cycle. The beneficial bacteria for any planted aquarium will be one that allows our plants to have healthy growth. This includes bacteria that bound different micro elements to make them available for plants (nitrogen is one example). So what does water plant need to grow? As they say picture is worth thousand words so here is one:

As one can see there is significant part of periodic table there. So where are those bacteria in this picture? Generally plants are not able to get nitrogen as a gas from atmosphere, bacteria is used to bound nitrogen into digestible form. Same thing goes for many other molecules. Plants are using leaves and roots to retrieve nutrients from the environment. The plants in aquarium are divided into two groups: real water plants and "fake" water plants. The real water plants will get most of the nutrients from the water column through the leaves, they have small root systems and grow pretty fast under water i.e. stem plants like hygrophilia or rotala. "Fake" plants will take most through the roots, they have big root systems and grow pretty slow under water i.e. echinodorus family. Knowing the plants you have will help you identifying best way to provide the required nutrients for your plants. On the picture you can see that the nutrients are divided into four groups: structural, macro, secondary and micro elements.

1. Structural elements
Most of the plant mass is build from structural elements: carbon, oxygen and hydrogen.
Those elements are required to build the main plant structure and energy deposits: sugars. Carbon is the most important component and represents about 60% of whole dry mass and it is consumed from CO2.  Hydrogen comes from water, oxygen from one of two sources depending on availability of light. When light is provided and photosynthesis occurs, it comes from water molecules. A side effect of this process is oxygenation of water. When light is off, plants "breath" by consuming oxygen diluted in water. Fortunately plants consume less oxygen than they produce in photosynthesis, that's why we have enough of it to breath. When light is turned off and you have fish, shrimps and other inhabitants in your aquarium, it is worth to aerate water. In this way you provide enough oxygen for plants and animals.

2. Macro elements 
Another ingredients required for plant growth are macro elements. Those are nitrogen, phosphor and potassium. Macro elements are used in all metabolic processes occurring in plant.
In water environment nitrogen exists in several forms: as a diluted gas, as ammonia (NH3/NH4), nitrite (NO2), and nitrate (NO3). Plants are not able to consume nitrogen in a gas form and ammonia and nitrite are toxic. These parameters should be kept as low as possible.  The most useful form of nitrogen in aquarium is nitrate. It is produced by bacteria in nitrogen cycle.
Phosphor also can not be consumed in raw form, plants get it from phosphate (PO4). PO4 is present in most fish food as well as is produced by dying leaves etc.
Potassium  can be consumed in its raw K+ form and can be provided in several forms i.e. as a liquid fertilizer.

3. Secondary elements and micro elements
Secondary and micro elements are required as a trace elements. Those are usually available in the soil or/and may be provided with a fertilizer.
In high concentration micro elements are toxic to fish, so make sure you follow the dosing instructions provided with fertilizer.


4. Light
That is the most important element, that a plant requires to grow. Without light and structural elements photosynthesis would be impossible.

Plant growth limits
A growth of plants can be limited by any of elements described above. That makes balancing an environment very challenging. If you have high-tech tank with lots of light, CO2 fertilization etc. but your iron level is too small, plants growth will be affected, leaves will loose colour etc. The same amount of iron in low-tech tank can be more than enough as light is already limiting factor. The outcome of this complexity is a fact that till now there is no one answer about how to fertilise plants and make environment algae free. There are multiple approaches for this and those I will pick up in next posts. This means that there is either too many elements available or at least one is limiting the growth.
Main thing to know about limit growth is that in most cases if one element has to limit growth it is best to choose PO4 for it. In environments where CO2 is limited or NO3 is limiting factor, algae growth is inevitable. Cyanobacteria is in most cases related to NO3 deprivation, CO2 is responsible for may types of algae and its supply is the most tricky to set up correctly. In the next post I will explain different methods that specify how much which element should be provided in aquarium to maximise plant growth and minimise algae.