Aquarium Plant Fertilization
Fertilization
of aquarium plants has been a problem from the start because of the
varied and specialized habitats that the plants come from. Aquatic
plants have special adaptations for the uptake of water and nutrients.
The watery environment also offers nutrients differently to normal
plants.
Nutrient Absorption
To know what nutrients to
give aquatic plants it will help to understand how they absorb
nutrients. Generally aquatic plants can absorb nutrients through their
leaves and their root systems unlike normal terrestrial plants that
absorb most of their nutrients from their roots.
Generally
aquatic plants have a very thin or no cuticle on their leaves and stems
as they are in no danger of drying out. This helps with absorption of
nutrients as well but also makes the plants more vulnerable to damage
and disease.
What Nutrients
All plants require an uninterrupted supply of 14 nutrient elements to grow properly.
These are the Macro-nutrients:
* nitrates (N)
* phosphates (P)
* calcium (Ca)
* chloride (Cl)
* sodium (Na)
* magnesium (Mg)
* potassium (K)
* sulfates (S)
And the micro-nutrients:
* iron (Fe)
* boron (
* copper (Cu)
* zinc (Zn)
* molybdenum (Mo)
* manganese (Mn)
All
these nutrients are needed by plants but the proportion they are given
to the plants in is where aquarium plants and normal plants differ. I
am not going to talk about each indivdual element but rather the macro
and micro-nutrients as a group.
Algae is the Enemy
Normal
fertilizer mixes made for garden and pot plants are made with large
quantities of the macro nutrients and small portions of the
micro-nutrients.
These are unsuitable for the aquarium. The main reason being that these cause algae blooms.
Algae
is one of the main problems in aquariums and is normally from incorrect
fertilization. Algae needs large quantities of macro nutrients and if
it gets these they will generally grow wild and cover the glass and
plants ruining your chances of getting a good looking aquarium and also
choking your plants.
Plant Fertilizer mixes
A good
aquarium plant fertilizer mix differs from a normal fertilizer by
having very few or no macro-nutrients. The main reason for this is
algae as mentioned above.
The macro-nutrients in the aquarium
should come from water changes (tap water normally has all these
nutrients in small amounts) and small amounts from the fish. Water
changes should be done at least every 2 weeks and about 15% should be
drained and replaced. This should supply sufficient macros.
The
micro-nutrients are different and are normally in short supply in tap
water. The other problem with the micro-nutrients is that they are very
unstable in their inorganic form and normally precipitate and become
unusable.
The Chelate Breakthrough
The discovery of an
organic molecule the chelate which binds to metal-ions tightly allowing
them to be dissolved in a water solution with no precipitation so
making the nutrient available to the plant. This very important for
aquatic plants which normally have a very large appetite for iron and
may need as much as 4ppm to allow healthy growth without chlorosis.
Chelate Types
There
are six types of chelates important to hydroponic growth but only two
that need to be mentioned for aquarium plants both for production and
in the aquarium.
EDTA (Ethylene-Diamene-Tetra-Acetic-acid) is
the first and most commonly known. This is not ideally suited for
aquatic plants because it is unstable at a higher pH than 6.0 and
generally aquarium conditions are between pH6.0 and pH8.0. This is also
a cheaper chelate and so is unfortunately used to cut costs, so
absorption is limited.
DTPA
(Dethylene-Triamine-Penta-Acetic-acid) would be a better choice and
should be more widely used because it is stable up to a pH of 7.5. This
is within the aquariums conditions.
A Good Aquarium Plant Fertilizer
When looking for a fertilizer as a very general rule look for:
1. Preferably a liquid
2. Low or No macro-nutrients
3. High Iron (Fe) in the chelated form
4. All the other micro-nutrients also in a chelated form if possible
There
is still a lot of experimentation needed in the aquarium but the plants
are getting to be of a higher quality all the time and people are
putting more time into the development of fertilizers.
It must
also be noted that fertilizers for the production of aquarium plants
are not suitable for the aquarium and will cause problems (mainly
algae).