Why do my plants keep dying?

Before the widespread publishing of Takashi Amano's Nature Aquarium series, successful and flourishing planted aquariums were mostly unknown in the west.  The European countries were experiencing great success although the aesthetics were much more like a well tended to garden as opposed to the Japanese nature model.  One of the biggest hurdles has been not just getting plants to live, but to thrive to the point that trimming becomes a necessity.  Because of the work of the Japanese and European aquarists, the information attained has been disseminated to the point that beautiful and artful aquariums with live plants are easily achievable.  The following points are the major contributing factors to being successful with plants.

Light

The driving process behind healthy plant growth is photosynthesis.  Plants use light to convert carbon compounds, as well as other elements, into tissue.  The amount of light needed to stimulate photosynthesis in aquariums dictates the use of high intensity formats.  Most hobbyists are using power compact lighting because of its relatively low cost and ease of use.  Many seasoned aquarists use metal halide lighting, which is more expensive and extremely intense.  The more intense the light that is being used then the greater the rate of photosynthesis will be.  With higher photosynthetic rates, trimming and fertilizing will become a regular activity.  More light usually allows a wider variety of plants to be kept.  However more moderate levels of light have proved to produce just as successful plant tanks.

Carbon Dioxide (CO₂)

Organic carbon is one the primary building blocks for plants.  It is present in water in four different associations:  free Carbon Dioxide (CO₂), Carbonic Acid (H₂CO₃), Bicarbonate (HCO₃^- ), and Carbonate (CO₃^2- ).  The ratio of these four different forms is proportionately the same.  CO₂ readily dissolves in water, however it diffuses very slowly.  This is why 90% of successful plant tanks are being supplemented with CO₂.  If there were a silver bullet for plant tanks, then CO₂ would be it.  There are two methods for introducing CO₂ to your aquarium.  The low-tech method consists of a fermentation process that produces CO₂ as a by- product.  This method is low cost but labor intensive.  Every two to three weeks the mixture is expired and needs to be cleaned out and a new batch mixed up.  However, many people use this method with great success.  The high-tech method consists of a compressed bottle of CO₂ gas, a regulator, and a Ph controller.  The high tech method is just about as hands off as you can get, as well as being hurtful to the wallet.  Depending on the size of the CO₂ bottle, the system might not have to be touched for a year.  Whichever method is utilized, a new level of success will be realized by using CO₂.

 

Nitrogen

Nitrogen is considered a macro element and is a part of amino acids, proteins, coenzymes, nucleic acids and chlorophyll.  It is integral to healthy growing plants.  When there is not enough Nitrogen, plants will develop yellow on their older leaves first.  This is because the plant is transporting the Nitrogen from the old leaves to produce new leaves.  Plants prefer Nitrogen in the form of Ammonium (NH₄⁺ ) 25% to Nitrate (NO₃- ) 75%.  This works out well because the fish in an appropriately stocked aquarium will provide the Ammonium and, with the help of bacteria, some of the Nitrate.  However, in a planted aquarium, the plants rapidly consume Nitrates.  When aquatic plants are no longer limited by light and carbon, they are then free to absorb Nitrate.  It often becomes necessary to add Nitrate to the tank to supplement the plants.  A situation can occur where nuisance algae will take over the tank when the plants do not have enough Nitrates to satisfy their rate of photosynthesis.  Nitrate is something that should be tested for weekly and adjusted accordingly.  A level of 5ppm to 10ppm should be considered enough.

 

Potassium

Potassium is also a macro element.  It is depleted quickly in a high light, CO2 supplemented plant aquarium.  Plants use Potassium extensively as an enzyme system activator.   When a deficiency of Potassium occurs, it will be expressed first in the older leaves.  Wilting edges and pinholes in the leaf are the symptoms of a Potassium deficiency.  This is because the plant is transporting Potassium from the old leaves to grow new leaves.  Although there is no conclusive or anecdotal evidence that elevated Potassium levels fuel algae growth, it is important that it be in proper proportions to Calcium and Magnesium.  Fortunately dosing Potassium without testing for it, rarely leads to problems.  This is convenient, because testing for Potassium is not easy.  Dosing schedules will have to be experimented with by the aquarist to determine what is best. 

 

Phosphorus

Phosphorus is the third macro-element.  It is a part of ATP, nucleic acids, phospho-lipids and some coenzymes.  Deficiencies of Phosphorus will be most obvious as a stunting of plant growth.  Severe deficiencies are expressed as a purpling of older leaves.  Too much Phosphorus will not only lead to nuisance algae growth, but also interfere with a plants ability to use Iron, Manganese, and Zinc appropriately.  Phosphorus is almost always satisfied as a by-product of feeding the fish.  However, aquariums with very intense light, many plants and a light fish load often need Phosphorus supplementation.  Phosphorus is easy to test for and should be done so weekly.  A Phosphorus level of 0.03 to 0.25 should be plenty. 

 

Minor & Trace Elements

Calcium, Magnesium, and Sulfur are the minor elements.  They are readily supplied and replenished with an appropriate water change schedule.  Iron, Manganese, Copper, Zinc, Molybdenum, Cobalt, and Boron are the trace elements.  These are also replenished with an appropriate water change schedule.  Since not all water sources are the same or trustworthy, using reverse osmosis and deionized water that is reconstituted affords the aquarist the most control.  Buffers are readily available that will supply the water with the proper amounts as well as proportions of minor and trace elements necessary for optimum plant growth.  Some aquarists use tap or well water with great success.  Others have nothing but algae and headaches.  Reconstituting RO/DI water takes the guess work out of fertilizing with minor and trace elements.

 

Conclusion

These are a few points that contribute significantly to a healthy growing planted aquarium.  For more detailed explanations or guidance on appropriate products to help apply this information, come in and visit with an AquaTouch employee.  Happy gardening!

Prepared by Scott Davidson