Well, according to Diana Walstad, a soil substrate will help to establish
anaerobic zones, which the plants like


They do? Why do the plants transport O2 to their Rhizosphere then?
They actively transport O2 to their roots and around each root.
This has got help many aerobic bateria in those areas/regions.

and which helps to keep iron
accessible.

But aren't you also adding that to the water column as well?
Anaerobic zones can also produce H2S if there is too much organic
matter in there.

I've always been puzzled by the fluorite-only approach. Obviously,
many people have good results with that. But I keep thinking that
fluorite-only (especially when combined with substrate heating)
would make it difficult for anaerobic zones to get established


Why do you assume anaerobic substrates are better or worse than
aerobic or sightly aerobic substrate types for plant roots in aquatic
systems?
Flourite w/o cables has pretty close to optimum flow rates. Cable add
too much.
RFUG worked great for me for a decade. That's pretty high flow.
The optimum figure for flow rate to best roots growth was about .49
liters per day of flow per meter squared. Not much.

Flourite is sandy iron rich clay. Clay has immense internal suface
area and extremely tiny pores and many binding sites.
If the clay is hardened, then kept at certain grain size, the outer
parts of each grain will be fairly aerobic but those tiny internal
pores will become anaerobic so there is a tiny micro habitat gradient
on each grain.
You'll see roots often boring into the grains.
Roots are very active.
But if the nutrients are also supplied in the water column, they will
not take up the nutreints through the roots very much, they will take
it in from leaves and stems mainly if there's enough in the water
column.
This has been shown to be the case specifically with a wide variety
oif aquatic plants.
Unless you look at those levels in the water column, it's difficult to
say what amount of interaction the substrate is truly having or not.

One way to test for this is to have a tank with half with and half
with something else for the substrate. Use the same plant etc.
A similar thing can be done for lighting temp colors, different
intensities etc.

(which,
according to Walstad, are one essential ingredient for healthy plants).
The owner of my LFS tells me that eleocharis acicularis will not grow
for him in a fluorite tank. He has two identical tanks that share a single
filter, one with a peat substrate and gravel, the other with fluorite only;
the hair grass won't grow well in the fluorite-only tank and eventually
dies off, whereas it's doing well in the tank with peat in the substrate.

Does great in my tanks. As a matter of fact, I have less trouble with
plant species in onyx/flourite tanks than any substrate I've tried,
I've tried all sorts of mixes.

Given that, in nature, plants grow in mud,

All plants do not grow in mud. Many grow in sand, rocky river beds
etc.
I know, I visit these plants/places in nature. The nicest looking beds
have rocks or sand. But there are also nice examples of mud based
substrates also.

I'm waiting for my digital underwater camera to try out next week.

it seems that soil or peat
would come closer to natural conditions than pure gravel or fluorite
substrates, and the good results they give would stand to reason.
(But there is the mess you get every time you uproot a plant --
not pretty.)

I hate the mess too. But Clay is natural and which is what the
flourite/onyx sand is, they don't "make it". It's just natural clay
ground up.
But I like peat, so I add a handful per sq ft to the bottom layer for
good measure to the onyx or flourite.

I've liked peat sub's better than soil.
I did like kitty litter(again, clay) and gravel, that was a winning
combo, but messy when you replant.
Relatively fast growing plants wear out soil in terrestrial pots in
about a year or less. Flourite never wears out, but you can add macro
nutrients to the water column also, just no urea or NH4.
The same thing can be done for soil sub's also.

I really like peat as an alternative to soil. I think the risks of
contamination with bacteria or parasites are lower, and you can
be sure that it won't contain added phosphates or urea. If you
water the peat for a week before putting it into the tank, you
get rid of most of the yellow color; once the peat is under the
gravel, it will leach little (if any) color into the tank. (I have a minute
shading of yellow in my tank, but you have to look closely along
the long axis through the water to pick it up.)

I agree, I get no discoloration personally, but I'm not adding as
much.
I got use to it years ago, so now I use yellow colored lighting to
mimic the effect:-)


If you want to keep blackwater fish, which like soft, acidic water,
the peat has the added bonus of helping to keep the pH low. And
the humic acids that leach out of the peat are considered useful too:
they inihibit bacterial blooms and diseases because they act as a
mild antiseptic.

I am really pro peat as well.
That low pH/humic acids will help produce a reductive substrate which
is important in release of those cations like Fe, not just anaerobic
conditions.
Once the plant roots become well established along with some organic
matter, the gravel does very well.

So a little both,
A little element of peat and a little of the flourite/onyx sand does
better than each does alone. Water column dosing and substrate dosing
of nutrients works best IME. Not just one method.

A side comment on the flourite tanks with the non CO2 low tech
approach, it works better IMO than soil and gets better as the tank
ages.
And I grew hairgrass and Gloss. But the Gloss did grow pretty slow, it
was great! The hairgrass went to town. No water changes, just feed the
fish. Once a month prunings.

Glad there are still peat folks left. I do add more peat when I know
it's going to be a non CO2 tank. I use ground peat about 1 inch dry
and 3-4 inches of flourite with lots of mulm mixed in. Not much
different than the CO2 enriched set up except for more peat.

Try it and see what you think.

Regards,
Tom Barr



Cheers,

Michi.