Re: substrate flow rate

[I seem to be getting a little emotional about this thread.  Please
take the following with a grain of salt.]

> From: spush_h at atc-1s_hac.com
> The peat is necessary to provide humic acids. The idea is to provide a
> uniform source of iron nutrients preferably at low cost. 

We need to provide a source of iron in a form easily usable by plants
(Fe++, not Fe+++) by root uptake AND leaf uptake.  It should be clear
to everyone here that a lot of plants (especially fast growing stem
plants like Rotala and Alternanthera sp.) don't really use their roots
for much nutrient uptake.  Plants that get nutrients through their
roots need the nurients to be bound to organic substances (chelated)
The uptake process (adsorption) has the root exchanging H+ ions for 
nutrient ions (or perhaps something more complicated than that).
Anyway, the chelated nutrients need to be in intimate contact with the
roots, not off in a user-conveninent tube somewhere.   

> Let's face it, the cost and trouble of daily iron feeding is high.

Oh, come on now.  Are you trying to start an Urban Myth here or just
repeating one?  A 250 ml bottle of Duplaplant-24 is $50 and has 
"5000" drops (their count, not mine).  A penny a drop.  Our 120
gallon tank gets 6 drops per day, $0.06 per day.  Feed the fish in
the morning, add 6 drops.  Where's the cost?  Where's the trouble?   

> How come you need drops anyhow if you have Laterite?

The iron in the laterite is being used by the plants and needs to be
replenished.  Iron also needs to be in solution in the water for
uptake by the plant leaves.  

Let's keep in mind that there are complex chemical processes taking
place in the substrate that go far beyond what we understand.  A rusty
ten-penny nail is not going to get you there. 

It might be useful to reconsider what is happening in natural plant
environments and try to synthesize ways to mimic that, rather than
creating some bizarre second derivative by developing cheap
alternatives of the techniques Dupla uses to mimic nature.

My impression of the direction the discussion is taking is that there
are three or four things that are recognized as important to a plant
tank that should (IMHO) be considered dependent on each other, as a
system.  Solutions are being proposed that treat each one
independently without regard to the overall system.