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RE: Roots

> What, again, is the reason to add an enriched
> substrate if you are going to add the required
> nutrients into the water column?

Mmmm, there is always a trade off. Balance is the key. All or nothing
attitudes will get you, in life and here. An example is the iron which seem
to help if there is also a supply in the substrate. Some root uptake does
help for certain nutrients more than others it seems to me. But there
argument against this also. Is it the bacterial interactions their effect or
is it simply the inorganic supply? Some may argue this for PO4, but I have
less and less evidence for this. Iron seems to have the largest potential at
high light for this to occur.

NH4 is a contentious nutrient, I tend to stay away from dosing this one in
any manner except fish waste(snails etc). Roots take this up, not sure how
much foliar uptake is done for NH4, not much I'd say, but roots can take in
both NO3 and NH4. Leaves generally take in only NO3.

I've spent a number of years not using anything other than mulm, with no
laterite/used RFUG filter which would blow out any accumulated nutrients and
focused on water column dosing exclusively. It works quite well actually. As
good as anyone's tanks using laterite and sand if not better. That's how I
learned the limits and possibilities of the water column dosing. I knew how
it reacts to algae and plants.

Some other things are going on in the substrate beside just having iron etc
down there I think. Bacterial interactions with roots and roots changes in
the substrate seems to be a very plausible cause(s).

I think that a good substrate is a place that provides a good medium for
bacteria-root interactions to take place. The better for the bacteria, the
better for the roots and hence the plants.

Most folks run their tanks lean, folks that don't use CO2 etc also will
benefit from a good nutrient rich substrate as well(A good source of
respired CO2).   

It seems that we
> could get maximum sized foliage for our set-up with
> the plant drawing all of its goodies from the water
> column. A plus in my book. It would also be a boon to
> the cause if there were minimal root growth for things
> like rearranging and gravel tidiness.

RFUG's are good for that, but I think this works at lower lighting values
much more effectively, at high values of light, one needs both methods of
fertilization, specifically for bacterial root mediated nutrient supply and
water column supply. As light values go up, more dependence on the water
column becomes necessary for nice plant growth.

But you can do 100% of either method at lower light, say 1.5-2watt a gallon
and have excellent results(and likely increasing to the point of
convergence). At higher lighting, things change. Plant assimilatory
efficiencies change also as light goes up(it declines).
Light has a large effect in some ways which I'll mumble about later in
another posting. 
> What would be the effect of a low-light situation on
> water column dosing with no enriched substrate.

This would work(does work) extremely well.

> IME,
> this doesn't work all that well. Granted I wasn't as
> patient with this scenario. It seems that algae was
> the better competitor in that realm.

But is it? I don't think it is. It does not match with my own tanks and I
have many years playing with this set up type(10).

> (not that you
> advocated this. I'm just wondering if you had any
> thoughts on the subject)

What I'm advocating is that substrates while somewhat important, are not the
end all or nearly as important in controlling algae as so many claim if you
use the water column within a range that is doable and flexible.

This works for high light or low light. At lower lighting, one gets more
efficient plant growth, less "leakiness", better color is some species
certainly, fuller leaves, slower growth etc. Less algae and slower uptake

They can be easier to dose if you are forgetful etc or run your tank at
"lean" levels. If folks prefer lean levels, they should focus on lower
lighting IMO. They will get better results, richer growth, less algae.

Limiting the water column by adding everything to the substrate doesn't
appear to be the main mechanism for limiting algae. If it was, where's my
algae? I've asked this before and no one ever gives any decent reason as to
why. But they always point back to algae being "limited". Yea, right. Try it
the next time you get Green water.

But........It(substrate dosing) is a useful tool in order to reduce the
dependence on water dosing and general forgetfulness. It also does work very
well and is low maintenance for lower light tanks also. But so does water
column dosing also and water column dosing works on many more plant types
compared to substrate only. Mixing both yield nice results. Don't fall into
the all or nothing trap but try to get an understanding or the relative
importance of each and how they interact and are interwoven.
Tom Barr  

> Thanks,
> John Wheeler