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[APD] RE: substrate eH investigation [technical, long]

> I'd be real curious to know if the eH in a rich substrate [see below] got
> down into the S reducing potential?

Well, you would need enough organic matter, reduce all the buffering
effects of laterite/iron, NO3 to push the Eh lower into this range.

> And if it did, were there negative
> side-effects?

Well, gets back to the issue of the plant's roots modifying their
Plants do well in aerobic and anaerobic soils. 

> parameters such as eH, then it has to consider toxins (see below Barko &
> Smart remarks) as well as nutrients. I'm inclined to think that using the
> most stable OM, peat (or humus/mulm) & keeping N & P only as simple salts
> occluded within clay would hopefully prevent the undesirable biochemical
> reactions. N is needed for bacteria to breakdown peat lignins further.

Well lignin breakdown is going to slow, no matter what. There is enough N&P
in peat and other OM for the bacteria.

This system is dominanted by microbial processes and root interactions. 
Al 3+ and H2S toxicity can occur but I would think it to rare in our tanks
unless you add a lot of OM.
That's the only way to get lower Eh's that would produce toxicity. 

> One of the problems with using a "messy" amendment like peat, soil or clay
> in a general substrate is that when you remove plants, you can liberate a
> lot of nutrients, perhaps even DOC and this seems to trigger BGA. At the
> least, it makes a mess.

Not if you do not add a lot of OM. Just enough to seed the gravel, enough
to provide some start up time till the naturally produced OM/mulm/fish
waste/plant matter takes over the cycle. 

In this manner you prevent new tank issues and the tank settles in nicely
for long term growth and health. 
You can test the water column if you so desire.
But the water column can be cvontrolled and maintained MUCH easier and
better than the substrate.
Just dose after the water change.

If you are really concerned about pulling anything up after
uprooting/replanting, heck dude, do a water change after you prune, that's
the best time anyway and exports any junk you pulled up.

I do not have much crud come up with the suggestions I give for Flourite
tanks. There's just not enough peat in there and mulm is in everyone's tank
anyway even if they don't add the peat.  

> If I put the same plants into ceramic pots, I can use much richer
> & simply lift the pots out to harvest them. Practically no mess at all
> you put the pot back into the tank, simply adding a little gravel to cover
> the hole made digging out a hunk of Crypts for example.

Yea, those pots will win the AGA contest for sure:)
These are good for the grower interested in dealing with rich substrates. I
do this on emergent growth plants.

I do not see the point submersed, the water column does all you need if you
have a good iron rich substrate.
Lot less messy too and easier to control, test etc etc.

Many plants simply do not use the substrate at all.Riccia, moss, ferns etc.
These are pretty popular, more so than Crypts perhaps.  

> Pots also help to prevent or forestall the tendency of some Crypts to
> throughout the tank. The problem with a pot containing C blassii is that
> eventually it becomes quite root bound & the plants do not attain their
> magnificent size.

You need to repot around every 4-12 months depending on the plant.
Nurseries have to do this. 

 On my website are pictures of C blassii which I grew
> several years ago; with leaves which were 2.75" wide and 11" long. The
> were about 17" on this plant so the overall length was about 28" and from
> healthy specimen it attained this size in only a few (4-6?) months. I
> think you can grow something like that hydroponically. 

Well, C cordata var blassii does not grow as big emergent, that's a simple
fact. You are comparing apples and oranges here. 

> A few years ago, I believe I gave Karen some C blassii which I think she
> might have shared with Neil Frank. I don't know if either have been
> successful in getting the large specimens. I seem to recall Neil saying
> something about not having red under leaf with other C blassii samples he
> had. Perhaps there are differences in the C cordata cultivars. Karen,

Yes, there are at least 3 varieties floating around.
Each with different ploidy counts. 

> In the deep cube tank I had a very deep substrate in those days. I know I
> had S reduction in there. It didn't come out unless I disturbed the
> substrate significantly such as by uprooting a giant Amazon Sword which I
> had there for a while. I think low redox is less of a problem than we
> think.

It depends on the OM content.

 I think it bothers plants not at all because their roots prevent low
> redox as they grow & penetrate. A freshly planted specimen might be
> susceptible I suppose but the plants seem to recover quickly growing new
> roots until the root-shoot ratio is back to what it should be. 

Yep. See those rotting Aponogeton bulb post that pop up.

> I think next time I try C blassii, I will use a 1 gallon or larger pot
and a
> mixture of peat & earthworm castings, fine steel wool or micronized iron
> a clay cap covered by gravel. Throw in some big clay-fertilizer balls;
> the heck! It might be wise to stay away from sulphate based nutrients.

Sounds gtood and will work.
I'd add some Ca/Mg, perhaps a little dolomite for this plant species.
It did very very well in hard water.

> Paul K uses trays, not too deep. Have you ever tried deep substrates Paul?
> Thomas, as you mention about a stable substrate, I think peat is a good
> candidate for providing organic matter & its pretty stable with virtually
> N or P available. Substrates with N and possibly P & of course Fe
> seem to grow big plants quickly. The deep substrate may even have
> contributed to a much higher CO2 concentration than I typically provide
> using injection. 

Perhaps.But this is mainly an issue if you do not add CO2. 
But you have to aslo conmsider there is simply more room and more bacterial
surface area etc in a deeper substrate, things do not have to be as
concentrated to contain the same amount of nutients. Flux in/out is reduced
Basically , the deeper substrate is a larger reservoir of nutrients.

The thing about an N enriched substrate is that its going
> to deplete over time so the dosing regime needs to be modified to a more
> hydroponic one. My two largest tanks are nearing 5 years & I've not
> them or changed the soil in the pots or in the other tanks with continuous
> substrates.

Use the ice cube method.
Freeze some soupy pre soaked soil in ice cube trays, insert deep under the
Do about 1/8 to 1/4 of a section in the tank at time each two weeks. 

> Initially, its probably easier to maintain an N enriched soil substrate
> because you don't need to worry so much about regular N dosing
> hydroponically. You get early great growth but the gotcha is that you may
> need to modify the regime to more frequent N dosing hydroponically. Crypts
> can get along fine with N limitation in the water but if you keep fish in
> the tanks and feed faster than the plants can grow, skimp on water
changes a
> little and you end up with BGA. :%]

Or another type of algae.

> Regarding organic content, you've mentioned some studies that indicate 20%
> OM is too high. The Barko & Smart study indicated that natural sediments
> above 5% OM had declining productivity. 

I'm taking this from Reddy et al, someone who I know, had a class with that
ate my brain and is specific for wetland plants and is one of the top
people on wetland soil research in this country.
This OM % content is for lakes with macrophytes.  

>I can't recall if the discussion
> suggested that low eH might have played a role; I've misplaced those
> somewhere in the move to this house. I recall they thought there might be
> some organic toxins such as aldehydes, alcohols that came into play in
> OM substrata.

Produced by frementors, but if the microbial loop is well formed, these
should also be broken down as well.

> When we talk about soil substrates, especially rich substrates, or deep
> substrates, its probably more of interest to specialists such as Crypt
> growers or for Lace plants.

So why do my plants get 24" long leaves?
Why does my C cordata Var blassii get 16-18" tall in a few months?

My substrates are not rich and do not have that low of Eh's. 

RFUG filters had similar effects.
C.c.var. Blasii flower submersed even in these tanks.

 Some recent increases in my N hydroponic levels
> for the benefit of the Lace plant, seem to have made the Crypts grow very
> fast too. I've moved away from fast growing plants primarily into Crypts,
> ferns (Bolbitus, Java) & Anubias but its trickier maintaining high fish
> bio-loads with those slow plants.

Get bigger tanks or remove the fish .......ahem, "bait":)

> Soil substrates aren't automatically bad for newbies; its just a different
> regime & I'm beginning to understand that it needs to change over time.

Yep. I do a modified version. I have folks add mulm(live bacteria from a
healthy estabished substrate and some OM) and peat.
I do not have folks add so much it causes issues when replanting. Mulm is
very safe as far as an additive, so is peat, so this is more fool proof.

Same with the water change/dosing routine I profess, easy, repeatable,
cheap, testable, stable, removes the organically bound unknowns/organics,
re sets the tank, less/no testing of NO3, K, PO4, Fe etc.

Tom Barr  

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