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Re: Indicator Plants
Andy Moore asked about techniques for using plants as nutrient
indicators in place of test kits.
Using soil substrates, strong lighting and CO2 injection together with
regular additions of K, Mg and Ca I find that I can encounter 3 kinds of
nutrient deficiencies at different times: N, Ca and Fe (or trace
nutrients) Each of these can be diagnosed and rectified without using
test kits but the methodology is slow.
Ca shortage can occur at times if I have a substrate with a lot of peat
and the time between water change is long enough that calcium levels
have gotten low. I make regular generous additions of Ca at water change
time and unless something (like peat or snails) is using up the Ca, I
would not expect a shortage. If I see poor growth and deformed new
leaves especially from a fast grower like Hygrophila polysperma and the
water change is overdue, I add some calcium carbonate (usually with a
water change) and watch for a week. If the symptom goes away, it was a
calcium shortage and I file it in my memory together with a theory about
why peat soaks up calcium.
There is enough potassium and magnesium supplied at water changes that I
don't expect to run short on these nutrients. A water change and a dose
of those minerals (premixed and dosed based upon water change volume)
keeps things happy. I do this kind of dosing without trying to diagnose
the cause. I'm not worried about overdosing either potassium or
magnesium and they are easily predissolved and easy to add to the water.
Nitrogen shortage and iron shortage can look similar. Poor growth and
yellow new leaves. Nitrogen shortage is the most common situation I'm
likely to encounter and I do have a nitrogen test kit so I usually cheat
and test for it before I add a dose. If I didn't have the test kit, I'd
add 1/8 tsp of potassium nitrate for each 10 gallons of water and watch
the plants for a week. If the plants perked up and grew better and the
yellowing disappeared, I'd conclude that it was a shortage of nitrogen.
Many kinds of nutrient shortages show as poor growth and yellow leaves.
You can get a clue about this if the nutrient is a mobile nutrient.
Mobile nutrient shortages show in old leaves and immobile nutrient
deficiencies show in the new leaves. Check out the nutrient deficiency
chart on the Krib.
I never had a shortage of iron when I was dosing with chelated
nutrients, either with Flourish or the chelated trace nutrients which we
get from the hydroponics store to prepare our/my version of PMDD. (other
folks here in Vancouver also get nutrients and instructions from me) In
recent years I have tried relying solely on the substrate for iron and
when I was using peat with various soils and clays, I never had a
shortage of Fe that I could diagnose as such. Peat seems to provide
enough natural chelating humins that there seems to be plenty of Fe to
keep the floating plants happy as well as the rooted plants. Almost any
kind of clay or soil with clay mixed into it even in tiny amounts is
capable of providing iron in the substrate. It turns out that the pH of
the substrate interstitial water is the major factor in determining the
concentration of dissolved Fe+++ there. Low pH increases iron
availability. The optimum substrate pH for nutrient availabilty is
between 6.5 and 7. Soils can be tested for their pH by mixing with
distilled (or low alkalinity) water and testing the pH after a few
Recently I used much less peat in a garden soil substrate and in this
situation I believe I can see poor growth in the newly planted stems of
the fast growing plants which can be cured by small doses of chelated
Fe. Since I used only a couple of double handfuls of peat in this
substrate, I never had a perceptible yellowing of the water. I wanted to
limit the humins in the water to see how little peat I could use. I also
didn't want to encourage green spot algae growth or BBA which I knew to
be on some of the plants I used. I did lightly bleach some of the plants
which I suspected -might- have green filament algae or oedogonium (green
peach fuzz-like algae)
Anyhow, the growth rates of the stem plant cuttings didn't take off like
I expected. I didn't add Fe in the first month because I wanted to test
if a nitrate addition would help. It did help somewhat and I theorize
that the plants started to get more Fe from the substrate as their root
systems had a chance to develop. I added a dose of Flourish (1 ml) a few
days ago and have been watching with interest especially the Salvinia
which has definite yellow small new leaves (but in the 75 gallon tank).
The Salvinia never stopped the yellow small leaves after the nitrate
additions so I began to suspect a lack of Fe in solution. So far it
looks as if the fast growing plants are responding to the Flourish
addition. Its difficult to be conclusive since the root systems continue
to grow and this may also be improving the ability of the plants to
extract Fe from the substrate. As well, the cuttings were small and will
grow more mass in proportion to their total mass. (apparent growth rate
increase but actually growth is measured as a factor of total biomass,
so-called doubling time) This means that subjectively, the growth rates
seem to improve although the doubling time may be constant.
The slow growing plants like Crypts, Swords, Anubias, Aponogeton are
root feeders and don't seem to be affected by the lack of iron in the
water. I don't know if addition of Fe in solution would help them as
much as other substrate fertilization tricks. This new garden topsoil
substrate is very low in nitrogen levels; I've added no fertilizer to
it; and consequently these slow growth type plants are growing steadily
but not rapidly. The roots will be developed enough soon that I will
fertilize only the Crypts and Anubias. I don't want huge Swords or
Aponogetons. All of these root growing plants respond to nitrate
additions in solution, but they respond even more to nitrate additions
in the substrate such as with clay fertilizer balls or Jobe's Sticks. I
think the phosphate addition in the substrate also helps them too. If
you used subsoil, clay and or peat without any topsoil, the substrate
probably won't have a lot of available phosphate or organic phosphate.
I'm not sure if peat is a source of organic phosphate. If it is, it is a
very slow release of phosphate because peat is pretty well leached and
the organic components have given up their easily broken down nutrients.
I figure regular topsoil can have varying amounts of organic material in
it depending upon whether the soil was enriched with compost in the
past. The phosphate content of topsoil is probably one of the most
variable nutrient factors and we need to guard against using a soil
which has too high a phosphate content. This is a good reason to use
subsoil instead of topsoil if you are concerned although I have used
substrates that probably had relatively high phosphate content
(earthworm castings). Not something for beginners as I did battle green
water with that substrate for a while although the plant growth rates
were very high.
Topsoil also has one other factor which I don't think has been discussed
much in this forum. I think it has the widest range of micro organisms
in it. In some ways thats good because there is a wide selection of
adaptable bacteria which are useful in breaking down organic matter into
nutrients. In other ways, it greatly increases the complexity of
interactions in the aquarium. This is probably not a big deal for plants
but it might be something to consider for fish stocks. I think its good
advise to colonize lightly with replaceable stock like live bearers for
the first month or two, just in case.
To play the devil's advocate for a moment, I'd like to make the point
that telling new folks that "watching the plants" is a good way to dose
plants may be misleading advice. The neophyte may be tempted to overdose
all sorts of nutrients especially chelated iron because he's trying to
find the magic bullet too quickly. You only need very very small
additions of chelated iron to the water. "Watching the plants" is a good
way to LEARN HOW TO adjust nutrient doses by watching the plants. Its a
learning process, not a _panacea_ (magic cure)!!
Its just as important to realize that there are no magic bullets that
will solve every algae problem either by nutrient dosing tricks or
adding algae eating critters of various descriptions. Beating algae is a
learning process too and you need learn to adapt the techniques that are
going to work for you.
Pocket lint is the real secret (as someone recently said)! Next time
someone asks you what is your secret to growing aquatic plants, you can
smile enigmatically and tell them smugly:
hee hee hee. :-)
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!!!