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Re: Dupla only?? + Steve's fertile substrate

> From: Olga Betts <sae at arts_ubc.ca>
> ....I think laterite has been demonstrated
> >as useful in the context of the Dupla strategy; <big snip> ....>Laterite
> works only because it is part of the whole Dupla system. If your goal is to
> avoid the commercial approach... <snip>
> how come experienced hobbyists have such good success using laterite
> in the subtrate and NOT the rest of the Dupla products?

I'm not saying that laterite can ONLY work with the Dupla system, I am
saying it works only because it IS part of a total system, the Dupla

By that I mean is that the overall strategy must include providing all
of the nutrients required by the plants. In the case of the Dupla
strategy, you have iron and trace nutrients being provided by the daily
Dupla drops. In the case of folks using laterite with other water
fertilizers such as TMG, I presume that the iron and trace nutrients are
being supplied by the Tropica Master Grow, PMDD or other preparations. 

Remember that several of these experienced hobbyists also use methods
such as Jobe's fertilizer sticks to add nitrate and phosphate in the
substrate! Now whatever system you use, whether the iron comes from the
water or the substrate, I contend that the ones which support better
plant growth do provide phosphate for the roots. Certainly CEC plays
some role but the phosphate ion is an anion, that is it has a negative
charge. Surface area and phosphate fixing ability may be more important
factors. I believe that it is not difficult at all to produce a suitable
substrate for growing plants. I believe that there are a whole lot of
materials which help capture and hold it in the substrate! Humus and
iron compounds are extremely common components of natural top soils.

Phosphorus is a macro nutrient and plants require almost as much
phosphorus as nitrogen. If we are successful in curtailing the amount of
phosphate in the water in order to limit algae growth, then we have to
expect that the plants will be getting the majority of their phosphorus
from the substrate. In fact, under natural conditions, phosphate is
extremely scarce in the water and I suppose that I why rooted plants
have specialized in extracting it with their roots.

I've wondered where these huge Salvinia plants come from that we
occasionally find in aquarium stores. When I bring them home and
propagate them floating, I always get plants only 4-5 mm across. A big
clue came when I started using Salvinia in my hyper-eutrophic killie
tanks. Suddenly I started getting BIG Salvinia!! In my large aquariums I
suspect there simply isn't enough phosphate available to the Salvinia.
My guess is that the huge specimens we see in the stores are actually
grown in eutrophic ponds or mud holes in full sunlight.

The largest Crypt wendtii that I ever grew were grown on an extremely
fertile 3 layer substrate which was a mixture of about 40 pounds of
gravel, 8 kg of iron rich pottery clay,  4 kg of earthworm castings,
about 5 kg of vermiculite and enriched with 60 grams of FTE and 150 ml
of Hanging Basket & Planter Fertilizer 14-14-14 Controlled Release
Fertilizer. Whoa!!! Very, very fertile but what a difference! This was a
very difficult substrate to work with. I had nitrate concentrations of
over 100 ppm. Phosphate concentration stayed relatively low at about 0.5
ppm (although I have trouble believing my own notes). Ammonia levels hit
1 ppm about a month after submergence so I added a biological filter and
the ammonia quickly subsided. I had to fight blue green algae and green
unicellular algae like pea soup. Some types of plants seemed to have
difficulty coping with the low redox and high nutrient concentrations in
this substrate especially after a pruning. Another problem with this
tank was the jungle like appearance it would get a couple of weeks after
each pruning. I had Crypts the size of medium sword plants. If I did it
again, I'd leave out the 14-14-14 fertilizer, most of the FTE and use
much less earthworm castings. I also probably won't use vermiculite
again since it makes a mess when uprooting plants. The aquarium was
stable for over a year and I only tore it down after it got infested
with a plague of Oedogonium (fur) algae when I was away on vacation for
2 months.

A word of caution: most phosphate compounds are very soluble. Organic
materials rapidly release their phosphates during decomposition. If
anyone feels that they simply must add phosphate fertilizer, I strongly
suggest that they follow the recommended procedures which have been
described previously in the APD and do the additions in small steps.

Passive techniques include:
 1) laterite (or similar ferrous substrate materials)
 2) fine texture materials (clay, loam, soil, kitty litter)

Active techniques include:
 1) small pieces of Jobe's sticks (which are occluded, that is designed
to prevent rapid release)
 2) clay balls with fertilizer inside
 3) low fertility soil preparations like soil soup
 4) fertile soils in pots with plants like Crypts or Swords

One also might use substrate heating coils, or very slow UG circulation
methods with the passive methods. (and probably ONLY with the passive

One last word of caution; beginners probably need to master the basic
husbandry techniques before experimenting with fertilizer in the
substrate. On the topic of basic husbandry, we've always assumed that
its better for beginners to use chelated iron dosing. I'm just
suggesting that MAYBE we should reconsider our first step advise. It
might be easier for newbies to follow a detailed but clear multi-step
procedure than to master the chelated iron dosing art.

For example, just because an iron test kit goes down to 0.1 ppm on the
low range, doesn't mean it's accurate enough to let you reach an optimum
iron concentration of say 0.16 ppm. On the contrary, some of these kits
seem to be quite inaccurate! Following the recommended dosing
instructions for some of the more concentrated fertilizers like Flourish
also can lead to excessive iron (in my experience)!

I also wonder if we do newbies a service by recommending 2-3 watts per
gallon. I know at _least_ one expert who recommends starting with low
light levels. Another famous expert gets lush growth using 1.6 watts per
gallon!! ;-)

Steve in snowy Vancouver (skiing soon; Yippee!!)