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[APD] Re: Dirt and OM

"What is "OM"? And no offense Tom, but your incomplete sentences are
sometimes very difficult to follow."

Organic matter. Peat, anything carbon based pretty much. Organic manures, soils, tree leaves and bark etc.
I type fast and sometimes miss things. 
I seldom edit. And it shows:)

" I personaly do not like using soils
because I do move plants around a lot, and a real rich top soil, super soil,
or potting soil will leech into the water colum as you said."

I have a similar beef. But a small amount say, 1/4" or less on the bottom and/or the use of mulm is useful and causes little to no mess. It's a carbon source for the bacteria and adds some reducing power till the tank settles in and the bacterial colonies are fully formed. 

I you wanted, you can do daily water changes, either manually or via an automated float valve set up and remove everything from the water column also if you have lots of rich substrate leeching or NH4 etc. 

This emulates a river/stream ecosystems fairly well.

 "Too much
decaying orgaics can cause problems such as creating a toxic gas and
depleting oxygen This is why "fired" clay substrates, (am I really going to
have to use the word "fired" every time I describe a clay substrate now?)
are considered safer and inert."

Well a balance of OM is needed, too much will cause sour spots(mulm accreation) and too little will not yield enough effect. Mulm can accumulate and cause issues also in older tanks. I think that, rather than compaction is what causes a substrate to wear out or needs to be redone. Some methods will deplete the macro nutrients and need to have them added back. 

"So let me ask you this Tom, is iron that important in the substrate? Do we
really need an endless supply of high concentrations of iron?"

I would say so, although I'm not entirely convinced. I would say with some plants, yes. Many don't care though. 
I've had non iron enriched substrates in the past. RFUG's. 

Getting a porous non iron rich substrate is possible, volcanic sands can be used without Fe. 
Then you could compare. 

" And if not,
what is it about Fluorite, (Flourite) that makes it such a great thing to
grow plants in?  If it supplies little else in the way of minerals, then
what is the big hubbabalu?  The only other thing it has going is cation
exchange capacity. With your method of adding everything to the water column
it really doesn't matter much what is in the substrate, right?"

I think it's more a question of cycling and the rates of turnover. 
I've said already recently what it is about porous substrates that give it the characters that help plant growth and roots. 

I seldom talk about CEC but am aware of it's role. I do not really see what it has to do with our plants though, the plant has access to the nutrient whether the substrate grabs it or it's in the water column.
It has to get into the water column to have the CEC take place so the plant has access in both places, locking it down in the substrate will not help or hurt. If there's Fe in the substrate, the way to get is Fe reduction. Roots or bacteria or low redox(peat/humic acids and tannins etc). 

Water column dosing will grow every plant we keep. Some show no differences with respect to the substrate. I used RFUG and sand for about a decade with plants. 
There's basically nothing in there except biofilms.

But __some plants__ seem to show differences with iron additions and then another level of difference when porous substrates are used on top of that. These difference appear more as you add more light and increase the RATE of growth. 

The rate of growth is a key part of any dosing routine/nutrient supply.  

The plants that show no differences are unaffected by using the iron and porous stuff. So they gain no real benefit.
Some plants might need extra Fe via the roots or at locations in the roots for good growth and color. 
I would feel confident saying this. 

"Best regards
Robert Hudson"

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