So now that you have a large selection of robust plants in a well lit tank, what are you going to feed them? Though it may not be obvious (since plants don't have mouths), plants do require a certain set of nutrients to be present for proper growth. In this month's column I'll explore two related topics: algae control and fertilization.
There are two types of nutrients that plants require: macro-nutrients and micro-nutrients. Macro-nutrients are nitrogen, phosphorus, and potassium. These are like the "meat and potatoes" of plant food, but not unlike humans, plants need a well balanced diet, this is where micro-nutrients come in to play. Micro-nutrients, or more commonly called trace elements, are what round out, or balance the plant's "diet". Trace elements consist of a whole group of substances including: iron, boron, manganese, molybdenum, zinc, and magnesium. The trace elements are used in minute quantities, and are essential for proper and healthy plant growth.
A good fertilizer will contain a balanced assortment of macro-nutrients and trace elements, but it should not necessarily contain phosphorous. Phosphorous causes a problem in the Dutch Aquarium - it promotes algae growth! This is one of the reasons why house plant fertilizer is not recommended for aquarium use. There many aquarium fertilizers available through pet stores and mail order sources. When buying a fertilizer make sure it has a good assortment of trace elements and that it doesn't contain any phosphorous which is usually present in fertilizer as phosphoric acid.
Fish are also an element of the Dutch Aquarium's fertilization system. The food you feed them gets converted into a complex and quite excellent fertilizer known as 'poop'. It is rich in both macro and micro-nutrients, and should be the plant's only source of phosphorous. It is important not to over-feed the fish population of a planted tank, otherwise an excess of phosphorous will be made available for algae to quickly develop on.
Carbon dioxide (CO2) is the final vital substance necessary for luscious plant growth. Though CO2 isn't technically a fertilizer, it is necessary for photosynthesis to occur, and it allows plants to much more quickly absorb and utilize nutrients. CO2 should naturally be available in the tank's water since it is exhaled by the fish and because it is naturally present in the air we breathe. Increasing the tank's CO2 level has been found to be the most effective way of increasing plant growth and essentially eliminating algae. Systems for injecting additional CO2 in to a tank can be as simple as using a pop bottle full of yeast and sugar water, to as complex as a compressed tank controlled by solenoids and a pH monitoring system. I would suggest starting with the simpler pop bottle system just to see how significantly your plant growth increases.
That's it for another month. I hope you've found this series on the Dutch Aquarium helpful, in the upcoming columns I'll explore different systems which will make your planted tank flourish and perhaps technically more advanced. Until next time - keep your plants in the tank, and your wet thumb green...