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Re: Aquatic Plants Digest V3 #124

On Fri, 6 Mar 1998, Simone Vicini wrote:

> Seen that I had no response to my previous posting I've tried to make it
> more interesting.

Gee, what do you do if noone responds to this one?

> I did not decided yet for my substrate but here are my condiderations.
> 1.I would use humus because it has very high CEC and because it is decayed
> organic matter so it should not cause any problem with high oxygen demand
> and with fast leaching situations. But beacuse its CEC it's totally
> dependant on Ph I will use also vermiculite and in greater amount, first of
> all beacause I will never menaged to pick up some humus in woods without
> picking up also some undecayed organic particles, second because it has the
> capacity to old nitrogenum in the form of ammonium, third because
> vermiculite has been reported to be a very good ingredient for substrates.

It looks to me like you've thought this out very well.

> 2.Maybe I will mix with that also some laterite (Dupla) first of all
> because it has some kind of AEC (anion exchange capability) second because
> it can make phosphates insoluble, then because laterite is a very good
> source of Fe and micronutrients 

Maybe this isn't such a great idea.  I don't know that you need anion 
exchange capacity for anything.  In nature, laterite and humus/organic 
material aren't found together; humus is found in the topsoil and 
laterite is found in the subsoil.  When you mix them it's possible that 
the low pH and low redox potential caused by the organic material will
cause the laterite to dissolve.  There wouldn't a lot of laterite 
dissolved, but it might be enough to turn your water red and create some 
pretty stubborn deposits.

> 3.I don't know if I'd better use a little amount of peat first to keep the
> Ph of this soil a little bit on the acid side second beacuse it has humic
> acids that can be usefull to plants even if peat is known to cause problem
> because is a decaying material wich has high oxygen demand, but probably I
> will solve this problem using a cable heater.

I don't know if there's much difference between peat and soil humus.  With
either ingredient, there's a chance that it will tint your water brown or
yellow.  The heater cables will increase the chance of that.  You can
counteract the color by using activated carbon in your filter.  Of course,
that might remove trace elements, as well. 

> 4.I will certainly use small gravel

I think if you try layering gravel over the peat/humus/vermiculite mix 
that you might have some trouble with the mix getting up into the water 
and the gravel sinking through the mix - the gravel is after all a lot 
heavier than the organic mix.  I've had luck with mixing a peat/potting 
soil mix with coarse gravel, and covering that mix with finer gravel.  
The coarse gravel holds peat/potting soil mix in place and keeps the finer 
gravel from working down.

Roger Miller