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fertilizing both substrate and water column
Henry Hatch asked:
> Also, I was interested getting opinions on the advisability of
> fertilizing both my substrate and water column ? Am I overdoing it ?
You don't make any distinction about which nutrients you think you might
want to add to your water column or your substrate. Some nutrients
really need to be in the water column. If you need to add them to your
water is another question since some of those nutrients may already be
present in your tap water.
Plants require several different nutrients. The following is from the
substrate article on my web site.
"Essential mineral nutrients are conveniently separated into two
categories. Nutrients used by plants in relatively large amounts are
termed macro-nutrients. Besides carbon (C), hydrogen (H) and oxygen (O),
they are nitrogen (N), phosphorus (P), sulphur (S), calcium (Ca),
magnesium (Mg) and potassium (K). Nutrients used by plants in small
amounts are termed micro-nutrients. They are iron (Fe), manganese (Mn),
copper (Cu), zinc (Zn), molybdenum (Mo), cobalt (Co), and boron (B).
Other mineral elements, such as sodium (Na), chlorine (Cl) and nickel
(Ni), are also present in plants, and may or may not be essential.
"It is possible to grow plants in completely inert substrates such as
plain gravel; however, it is common to use a nutrient strategy where
some or most of the nutrients are obtained from the substrate. This has
several benefits. Many nutrients are absorbed preferentially by plant
roots. This means that plants can grow faster when nutrients are
provided in the substrate. We can limit the nutrients that are dissolved
in the aquarium water to restrict algae growth. We can employ higher
concentrations of some nutrients in certain kinds of substrates and thus
get improved growth rates. It is not necessary to perform nutrient
additions as frequently nor to measure nutrient levels in the water as
"On the other hand, it may be necessary to take precautions when using
various additives intended to produce more fertile substrates. The
substrate should be prepared so that excessive amounts of phosphates,
nitrates or ammonia are not released into the aquarium water. The use of
excessive amounts of organic materials or the wrong types may result in
high rates of bacteriological decomposition that consumes oxygen in the
substrate and may release harmful substances. Different aquatic plants
are adapted to different types of substrates. Organic plant materials
such as leaf mulch, peat, composted particles of wood release a variety
of humic acids. Some soil amendments may contain excessive amounts of
some minerals that can interfere with nutrient uptake by plants or be
toxic to invertebrates (snails) or fish."
It is not uncommon to supply micro-nutrients (Fe, Mn, Cu, Zn, Mo, Co, B)
in the substrate. In fact, these nutrients are available in most common,
ordinary soils. I would suggest that it is advisable to choose a well
Some nutrients (K, Ca, Mg) are only utilized effectively by aquatic
plants when dissolved in the water column. CO2 also probably falls in
For our purposes it makes little difference to most plants if you supply
N or P in the substrate or in the water column. Those nutrients quickly
move into the water column under most circumstances. Seldom is it our
goal to stimulate really high rates of growth EXCEPT for certain plants
which are notoriously difficult and slow growing. Ordinary soil with no
added N or P seems to be fine for most of the Crypts that I've
encountered so far. I've found it very helpful to fertilize C nurii with
fertilized clay balls; perhaps this is a plant which is really only
adapted to emersed growth in relatively fertile conditions. I've been
told that its an order of magnitude easier to grow Crypts under emersed
conditions (but that's not my goal).
I think Cabomba is a plant which really benefits from growth in a
fertile mud. It probably has other strict requirements as well. The
rapid growth rate of this plant when it is properly growing probably
makes it unsuitable in an aquatic garden. I have a feeling the reason
this plant used to be sold so commonly is that it is very easy to grow
in huge amounts under sunlight and its pretty enough that it was a good
seller. Now, I seldom see it in aquarium stores because its of its
notoriety as a difficult plant.
If you want to grow a rather large centre piece plant such as a big
Echinodorus, the use of extra substrate fertilization can be very
useful. Don't forget to keep these plants well fed with calcium too.
We should also not forget that we supply large amounts of S, N and P in
the form of fish food. These minerals are very rapidly liberated as the
fish feces decay or are respired by the fish in the form of ammonia. In
my soil aquariums, I presently do not use any N or P additives (except
for my C nurii) since there are adequate supplies of these minerals from
the fish food. I do have to keep on top of the K, Mg and Ca. CO2 is also
a critical nutrient but this is adequately and continuously supplied by
a cylinder of compressed CO2 gas so I don't have to worry about this
except to clean my powerhead inlet filters every week or two.
So far I have not had to make any micro-nutrient additions. In fact, due
to the peat releasing humic acids which chelate reduced iron from my
substrate, I suspect that I have relatively high levels of
micro-nutrients in solution. Considerably more than we might encounter
in natural biotopes. Currently its not causing a problem with algae
although I have more surface algae than I'd like. I think a lot more
water changes would help and a continuous water change system would be
very nice to have. With a continuous water change system, I might be
able to dispense with Ca, Mg and K additions too.
If micro-nutrient supplements are readily available to you and you can
afford an iron test kit, it may be simpler and easier for you to perform
daily or weekly micro-nutrient fertilization, that it would be to set up
a soil substrate. I suspect that it would be much simpler for the
beginners if all of us experts would agree that one particular regimin
was the easiest. :-) If you're following the Dupla style or the PMDD
method, you probably should just use gravel or gravel with laterite or
gravel with clay. You should NEVER overdo the fertilizers in the
substrate in any event, but sometimes they can really help you with
Is adding micro-nutrients to the water in addition to having soil
Is it harmful? Probably not. (unless you have an excess)
Is it beneficial? In all likely hood no but it might be. It depends if
you have a shortage of one micro-nutrient.
If you are growing plants are a certain regimen and its working fairly
well for you but eventually you observe some symptom that you think
-might- indicate a shortage of a particular micro-nutrient, you can add
an appropriate dosage of that nutrient and see if the symptom goes away
or if growth improves. Be careful you don't fool yourself by adding
anything else at the same time such as with a water change though...
Steve Pushak Vancouver, BC, CANADA
Visit "Steve's Aquatic Page" http://home.infinet.net/teban/
for LOTS of pics, tips and links for aquatic gardening!!!