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Re: laterite, et al
> Date: Mon, 29 Dec 1997 21:04:03 -0800
> From: Stephen Pushak <teban at powersonic_bc.ca>
> > What is the proper level of CEC in the substrate?
> There is no such thing as a proper level of CEC.
But more [than laterite] is better, according to your theory? If I may
summarize your original first paragraph:
"... laterite has a relatively low CEC ... Improving the CEC of your substrate
is quite easy ... [improvement methods listed]"
If there is no such thing as a proper level of CEC, why are you trying so hard
to convince the readers of APD that laterite does not have enough?
> It is well understood
> that soils with a higher CEC value are better able to retain nutrients.
I've never argued with this fact since that's pretty much the definition of CEC.
What you keep implying is that a substrate needs a higher CEC than laterite
provides to retain enough nutrients for good plant growth. This, to my
knowledge, has not been proven anywhere. Quite the contrary, good plant growth
with a laterite based substrate has been demonstrated at the hobbyist level by
many people, including myself. Let the readers judge for themselves; my website
is http://www.frii.com/~booth/. Dueling web sites at 20 paces. <g>
> There is a table of CEC values for various substances in my
> substrate article. Please note that laterite also has a CEC value.
I wish you would note that also. Which gets us back to the original question:
why do you think this number is too low for aquatic gardening purposes?
> of the major points of my post was that laterite and kitty litter are
> quite different in their characteristics.
Your first couple of sentences mentioned that. The major point of your post
seemed to be that phosphate may be lacking in the substrate (or your substrate,
at least), leading to the need for Jobe's plant sticks. Yet, a laterite based
substrate helps sequester phosphate right where it's needed. Go figure.
> I have never heard of specific plants requiring a specific CEC value.
> I'm not familiar with the laboratory techniques for measuring CEC and I
> don't think we should mislead people into thinking there is any value in
> attempting to measure it.
Yet you suggest that more CEC is better and give us many techniques for adding
CEC. Maybe I'm alone in my belief, but I think one should have some measure of
how much CEC is already there and how much CEC is actually needed before one
starts adding extra CEC to an aquarium. Luckily, I believe that Dupla knows how
much CEC is needed and I follow their instructions for adding it with the proper
amount of Duplarit-G.
> I don't believe that the CEC of laterite is it's key advantage. You are
> pretty quick to criticize empirical results as non-scientific but we
> should remember that the only evidence we have about laterite is
> empirical. We can only surmise that laterite and other substances help
> to bind phosphates in the substrate.
I am pretty quick to criticize empirical data masquarading as scientific data.
If I have ever couched any claims about laterite as other than empirical, I
would appreciate knowing about it. I am not a scientist but my wife is, so I
know what science is about and I am pretty careful how I phrase things in this
forum so as to not imply any scientific results.
> Yes, experiments by Barko and Smart clearly indicate that sediments with
> higher than 5% organic content actually inhibit growth. Sediments with
> lower than 5% organic content grew plants better as the organic content
You are implying that organic content is good if kept below 5%. How do mere
hobbyists determine organic content already in the substrate and how much of
what is needed to get to 5%?
> > Is this by weight or volume?
> By weight.
> > I have 200 pounds of gravel. Does this mean I need 2 to 10
> > pounds of humic material?
> No. Your layer of gravel is probably too deep for that. I would suggest
> that it would be more appropriate to use a layered approach similar to
> what is advocated for laterite.
I don't believe you've mentioned depth before. Mine is 3.5" deep. What's the
deepness limit for using humic material?
> > This doesn't jive with my experiences with massive plant growth using plain
> > gravel substrates, undergravel filters and Dupla fertilizers.
> You are assuming that your Dupla substrates are infertile. If your
> substrate helps to grow better aquatic plants, it can only be because it
> is fertile. Any other theories?
"Infertile" is your definition, not mine. Maybe we need some new definitions or
terms that aren't quite so loaded with implication. How about:
Dupla-style: "just right"
Fertile: "loaded time bomb"
> I will qualify really high lighting to mean 4+ wpg or partial sunlight
> and significant chelated iron to be greater than 0.2 ppm.
Yeah, I would qualify those as pretty extreme since the general recommendation
is 2-3 wpg and 0.15 ppm.
> If your aquarium is in the range of 1-2
> wpg, then you probably won't need the high quality iron test kit that
> George needs. ;-)
Guess I better trade mine in for a low quality kit since I have 1.6 wpg. :-}
And what on earth does iron test kit quality have to with anything?
> > Let us know when you find a substrate recipe that works for more
> > than a few months.
> I have George. Since when did we make a rule that says you're not
> allowed to periodically fertilize the substrate?
If your recipe was the 96 step process you posted a while ago, I guess I'll just
stick with my infertile, unoptimal methods.