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Re: long term subtrate experience
<< Date: Fri, 11 Apr 1997 10:56:55 -0400 From: Michael Eckardt
<mike at odg_com> Subject: long term subtrate experience
I have been wondering how long the substrate of a planted tank is
viable.
So the questions are:
What are your long term (i.e. > 2 years) experiences with your
substrate? Should the Dupla style of substrate be recommended for
anticipated long-term setups? Are the "rich" substrates more
appropriate for shorter term setups, experimental tanks, or plant
propagation tanks? >>
I think the whole point of the Dupla system is to provide constant
conditions as much as possible and this is one of the big advantages.
With the "richer" substrates, you will always notice changing
conditions related to nutrient levels and long effects which are
difficult to measure or identify; I'm talking about organic substrates
here. If you were using chemical fertilizers in sand/clay/(?) you
might be able to maintain more consistent levels by periodically
adding clay enriched balls or sticks or some such thing. Still, you've
got to wonder what happens to the sulfates in those chemicals. I
suppose that a lot of the sulphate will be either consumed by the
plants or removed with water changes as a dissolved salt.
When we talk about "rich" substrates, I think a lot of people have a
misconception about what this means. By terrestrial standards, this is
not a rich soil at all. Undecomposed manure, organic material etc has
the potential for creating some REALLY bad conditions. Probably what
you want is organic material which has gone all the way to becoming
humus and is really not that rich. That will give you a high CEC and a
low fertility which will not change a lot with time. You won't have
the high levels of nutrients that you have to be concerned about with
most of the organic materials which you are forced to choose from.
From this perspective, perhaps the best choice would be natural soil;
soil which has sat for many years in an undisturbed condition. No
manure; no compost. But that may not be easy to find especially when
you live in a city and you're stuck in the mountains with a lot of
glacial till for local soil. The second best choice might be earthworm
castings (EWC) or peat. It turns out that neither of these is very
completely composted (but much better than manures) and so you're
still going to have a LOT of biological activity happening for about a
year. Then it would probably settle down and become a "low" fertility
substrate that is pretty stable. Of course, you can still add
fertilizer to the substrate by other means and you still have fish
poop and detritus.
The thing about a fertile organic substrate is that it has a lot of
nutrients especially nitrogen that can really give your plants a kick.
The problem is that there is a much larger potential for things to go
wrong. Really wrong.
Let me describe some scenarios I've experienced with small tanks. I
set these 2 gallon tanks up as quarantine tanks for plants after
bleaching so I could observe the plants to be sure that all the algae
was gone. Sounds like a great idea in theory but in practice both have
turned out to be disasters. Don't feel too bad; what's bad for me has
turned out to be good object lessons for y'all.
The first tank had several Crypts after a short bleach treatment in an
early experimental clay/EWC/sand substrate with clay fertilizer balls.
The big problem was there was way too much fertilizer in there and it
turned into a mush of BG algae. Also I couldn't fertilize with CO2 and
so I tried using an airstone to circulate the water. Everything turned
to mush but the Crypts being adapted to such horrible environments
took it in stride, melted all their leaves but the thick roots
remained alive. After a lot of washing, I transfered the remnants to a
large tank and they did recover quite nicely. This would not have
worked with any other plant I suspect.
The second tank was another experimental clay/EWC/sand substrate with
only 6 granules of fertilizer. This time I rigged up an inverted jar
in the corner using a coat hanger and bubbled yeast CO2 in. I also had
daphnia and lots of snails to eat the algae. I added 4 lightly (60
sec) bleached baby Echinodorus osirus specimens and all went fine for
a few weeks. The plants showed moderate growth with new leaves. The
CO2 acidified the water and the daphnia all died. Ok, no big deal. The
water wasn't green anyhow. Heavy growth of algae on the sides since
this tank was on a shelf close to the big MH light and getting plenty
of light. (not a good idea) This made the snail get very big and fat
and they laid LOTS of eggs all over the leaves of the plants. Oh-oh. I
took two of them out since there appeared to be no sign of the
original algae and the plants looked like they had established some
roots. I washed the snail spawn off as good as possible and planted
them. I notice that the old leaves seem to have suffered some melting
or damage perhaps from the snail spawn or my treatment of the plants
with rubbing and cleaning. Both are alive although touch and go.
Not so good for the other two. After the disturbance in the tank, the
water was VERY cloudy from the clay. I didn't panic; figured it would
settle in a day or two and added more daphnia and small amount of
organic water to help the clay to settle. After about a week, the clay
still has not settled and deprived of light, the plantlets could no
longer produce oxygen and I reckon their roots succumbed to toxic
stuff produced in this "rich" substrate. When I pulled them last night
there wasn't much left. There were these brown things that once might
have been plants but were now mostly mush.
Now and experiment that worked. A small margarine container was filled
with a mixture of local clay, sand and the washings from the EWC soil
as per Paul Krombholz's method for preparing soil. This method removes
almost all of the organic material from the EWC soil since it's still
fibrous and too large to pass through a screen. It was a laborious
process. I think I enriched it a little with some EWC or fertilizer;
can't remember. Put in a layer of white silica sand and a small Crypt
and kept adding water carefully and its been sitting to one side under
the strong MH light. It's not huge but its healthy and the leaves
alternate between being submerged and emerged. I might repot this into
a regular flower pot and try growing it as a terrestrial plant for a
while just to see if it will live and maybe flower.
Lessons:
A) be careful with clay; get a cloud of it and you can kill off your
plants and fish if you have a transitional organic tank. (one that is
still in the process of heavy decomposition) Prevent light from
getting to the leaves and they stop photosynthesizing and have no
protection via oxygen in their roots. In a quarantine tank, maybe
don't even bother with clay at all.
B) a rich transitional tank is no place for a few small plant cuttings
that are possibly recovering from bleach. Far better to have a small,
established natural soil, or fine gravel tank with CO2 and low
nutrients for a plant quarantine. Probably the best way to do that is
with a tank full of H poly to keep the soil sweet or to condition
it...
C) less is better; less clay, less labile organic material, less
nutrients, less CO2, less light. A 20 watt compact FL probably has all
the light you need.
C) a small tank is no place to be fooling around with an unstable
system. A fine gravel tank filled with water from your main tank
probably has all the nutrients you could need.
I wish we had a better way to deal with removing organic material from
soils than the laborious method of trying to force it through a
screen. Maybe my EWC just has too much fibrous material in it and I
should use regular dirt. I think that's also why Paul doesn't see the
high nitrogen levels from his soils that I do. He uses liquid nutrient
extractions made from soil and compost that are very powerful and
added in small doses.
Steve Pushak in Vancouver where spring is temporarily on hold