Author: Dr. L.E. Freese
every gardener knows, fertilization of the soil is essential for the
growth of plants should this then not be a logical assumption for their
The common believe is that
the plants in an aquarium have enough to feed on from the waste products
of the fish and that too many nutrients are the cause of algae blooms.
This is sadly not always the case, as the nutrients that are released
often favour algae growth rather than plant growth.
Contrary to popular belief fertilizing your aquatic flora does not necessarily lead to an increase of algae, but can inhibit the growth of it. Studies have shown that if the nutrients in the water are in a ratio that the phosphate is present in a lower concentration than the other nutrients, the higher plants outcompete the algae for the phosphate and thus the algae concentration diminishes.
The nutrients that are
required by the plants can be divided in macro- and micronutrients. The
macronutrients (Nitrogen, Potassium and Phosphorous) are elements that
the plant uses the most of, the micronutrients (Iron, Magnesium,
Manganese, Boron, etc.) on the other hand are only utilised by the
plants in small quantities. The micronutrients are present in tapwater,
but there may be some that are deficient depending on the area where you
live, therefore it is essential that they are added to the aquarium.
Micronutrients need to be replaced frequently due to their unstable
nature in water. Iron for example rusts (oxidizes) and in so doing
becomes unavailable to the plants. The Iron that I present in
fertilizers should be in a chelated form, as this does not oxidize and
therefore is available to the plant for longer periods of time.
The proper levels of
nutrients that need to be added to the aquarium varies depending on the
fish and plant load, water chemistry, water change frequency and
lighting. It is therefore best to follow the instructions of the
fertilizer used and then experiment with the dosages if the desired
results are not attained. A common mistake is to expect miracles; the
plants will not react immediately, but will require a month or two for
the change to be noticeable.
There are 2 methods of
fertilizing your plants: substrate and liquid fertilization. The
aquarium can be fertilized with tablets, powder or sticks that are added
deep into the substrate and they slowly release their nutrients over a
period of time. The advantage of this method is that the nutrients are
available to the roots and the water column is not affected. Liquid
fertilization needs to be added frequently (daily or weekly) and the
advantage is that the micronutrients levels can be upheld and there are
plants that do not have roots that enter the substrate and absorb their
nutrients from the water.
In conclusion there are a few
things to remember; firstly never add a fertilizer to the aquarium that
does not state the components of it, as you may be adding something to
the water that is harmful to fish. Secondly do not use garden
fertilizer, as they contain urea which is essentially ammonia and this
is deadly to fish. Garden fertilizer contains high levels of phosphates,
which will cause an algae bloom and thus decrease the visual pleasure of
a planted aquarium. Lastly certain micronutrients may accumulate in the
aquarium and this could lead to complications with the fish in the
water, by doing 25% water changes every 2 weeks this dilemma can be