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[APD] Re: Thoughts on subs, mature vs new tanks
"George & I had a little debate a few years back about flow induction from
substrate cables. I pointed out that if you examine the thermodynamic
properties of water & substrate that it was unlikely that any appreciable
flow is generated by substrate heating cables. The temperature gradients are
just not enough to counter the viscosity effects within the substrate.
To my knowledge, no one has ever measured flow rates from substrate heating
cables. There is a way to do it if someone is interested. See archives."
I think Claus did. They measured one tank and played with flow rate optimiums.
But rather than expression this as flow rate, redox may be more useful.
Slowly pushing a redox probe into different substrate set ups would tell you pretty much all you'd need to know for optimal diffusion /in/out of the substrate as far as plants are concerned.
"I expect that the benefits of cables are entirely as you stated, caused by
increased microbial activity from higher temperature."
Well, I think the cables may help out in the start up phase of a plant tank. It may reduce the spikes of NH4 and build up some FePO4 for the roots since the Dupla approach would rather have the water column clean/very low nutrient and the substrate the source of PO4.
>From that prespective, the cables would help start up a tank reasonably well. The increased flow rate would help bring some organic matter to the substrate to help the other colonies of bacteria that are associated with the nuterient cycling that occurs in the substrate that NORMALLY are not in large densities withoyut this added Organic matter.
This is perhaps the main "why" we see older mature tanks that do very well even if we disturb things every now and then and if you disturb things too much, then you upset these layers and get an algae bloom.
This is also part of why we see tanks start up very well when a little peat is added along with Mulm.
This adds precisely what is lacking in a new tank and a long term organic source of carbon(peat) and it also lowers the redox slightly to get the substrae environment going till other processes take over and keep it lower in the gravel.
If you take this increase flow rate to the next level and keep increasing it, say using a RFUG filter, then you see a similar start up pattern and more reliance on aerobic processes and also the ability to keep higher fish loads/prune heavily without much algae blooms.
But I think if folks want to look at flow rates critically therough a substrate, you need to try several ranges of flow.........not just diffusion and cables but also the higher end.
Most test involve a low, medium and high range of the parameter of interest.
"We know that Fe reduction occurs in a mineral soil substrate with very
little organic matter because we can observe the deposition of iron oxide on
the glass at the interface with higher oxygen levels."
This layer is simply higher near the surface if you add more organic material, deeper if you add less.
But you also can consider denitrification and Mn reduction.
" Soil with a very low
organic content is all you need such as topsoil prepared using the Krombholz
soil-soup method. In a nutshell, you mix the soil with water to make a runny
pudding and pass it through screens to remove the bulk of the large organic
material. You can also supplement the soil with some peat to increase the
organic content without creating a danger of an extremely low redox. This
will extend the time that the substrate remains productive."
I think mulm is better than this. It has precisely the stuff that a mature tank has, all the bacteria, benign organic material(relatively) and is less work to make/more fool proof.
"After a period of time, plant roots can so fill a substrate that the redox
potential is no longer low enough to reduce iron. This is because the
substrate depth is relatively shallow and plant roots convey oxygen into the
If you consider the micro pore spaces in a porous grain like Flourite, these regions are preserved even if you bring the grain up from 10cm deep.
Also, there are many places in the substrate the roots never quite make it too unless you never prune or have very weedy/rooty plants.
The micro sites are important and many plant roots wil bore into these grains to get at these reduced cation nutrients(Eg Aubias).
"To my knowledge, no one has directly measured eH (redox potential) in
aquarium substrates although Diana Walstad & I briefly talked about it. It
would require some very specialized equipment that might be available in a
university setting. Tom, is that equipment available to you?
Yes, they have a wetland soils lab with micro redox probes, platinum electrodes, pH etc that can be pushed down slowly into the substrate for measurement.
But you need to measure organic matter, Fe, NO3 etc.
I'd rather assume that the other plants already measured and had research done on them as far as growth in these systems is similar to aquarium plant preferences.
I think based on what I've seen in aquariums that MOST PLANTS have very similar needs as far as nutrients when using CO2 and dosing methods. Having grown 250+ species over the years, I've seen this pattern.
I think if you look at wetland plant charateristic preferences for redox, that will give you a good close answer.
But plants will modify their surroundings so this may not mean much as far as the plants really are concerned.
We might be able to expain some things with this, but I think it will not really help an aquarist/plant hobbyist day to day.
A lot of work also.
I avoid that if I can:-)
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