[APD] Re: Flourite vs dirt

[Thomas Barr <tcbiii at earthlink_net>]

>Using large amounts of top soil can be dangerous in an aquarium because the
>decaying organics can cause problems. 

Well, yes and no.
NH4, depletion of the O2 levels by bacteria catabolizing the OM and Reduction of SO4 are the only negative things really that can occur in significant amounts.

This can be addressed by soaking or boiling for sometime prior to use.  

>Diana Walstad does appear to favor
>using top soils without being concerned of that fact. That is what she talks
>about in my forum.  However, I presume she limits it to small amounts under
>a layer of gravel, but I have never discussed this with her so you would be
>better off aasking her directly.

Well, when you consider non CO2 methods and the lack of dosing and reliance on fish waste, it makes sense to add more OM to the substrate.

The rate of growth is the question between these methods. 
Substrates have no problems supplying enough nutrients along with SUBSTANTIAL amounts from the water column and NPK, traces from FISH food and waste.

I do not do water changes for 3-6 months so all that fish waste is going somewhere, and the amout of this waste is consider, perhaps more than the volume of the soil itself in most of my non CO2 tanks certainly.

How much nutrient content is really coming from the soil vs the water column after a 1 year?
I'd say perhaps for the first few months, 3-6 or a lot does come from the soil, but there after it's coming in from the waste/fish food.

By adding more OM, this provides a long term anaerobic layer, this preserves the nutirents from being broken down, but a layer will be denitifying all your Nitrogen right out of there, so the nitrogen issue after a few months, perhaps even less is depeleted unless the plant roots get to it. NO3=>N2 gas occurs at moderately reduced Eh levels, about 100-200 mv. 
DBS and plenums try to achieve this without going too anaeroic in the deepest layer and producing sulfur reduction.

It's a balance in the substrate also.

If you do not uproot and replant often, then a little extra soil is not going to make mess constantly either.
If you only uproot once every 3-6 months and you also do your water at that time also, then this is not an issue.

While many like to suggest that soil, and the substrate supply all these nutrients, the cycling issue and the inputs from fish waste or dosing really seems to be much more significant, even in non CO2 tanks.

Much of what is placed into the substrate is leeched out, slowly perhaps in some cases, but most of it fluxes out into the water column over time.

Just because you are unable to read a measurement, does not mean it's not leaking out slowly and being used up before you can measure it.

Tracer studies are useful for uncovering these types of questions. 
Not a hobbyist thing mind you, but some inferences can be made and simple two box models of inputs and outputs can be done also in our own tanks.

Regards, 
Tom Barr

>Robert Hudson




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