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Re: Aquatic Plants Digest V3 #329

Steve Pushak clarified:

> I don't believe I said that the transpiration stream of submerged
> aquatics is responsible for aeration of the substrate.

Oops, sorry if I overextended things bit.

> ------------------------------

Bob Dixon wrote:


> Does this
> exchange site become useless once the hydrogen is on it, or do natural forces
> like electronegativity cause the hydrogen to them be replaced by the nutrients
> we are attempting to provide?  And if the latter, how does the plant overcome
> these forces to get the hydrogen back on and the nutrient back off?  Or is
> that second question too complex to answer in a single email?

As I understand it, the hydrogen usually stays on the site only briefly
before it is naturally replaced by an ion from solution.  The ion that
replaces the hydrogen (Ca++, Mg++, Na+, K+, NH3+) is available to plants.
If there's no circulation then eventually you run out of nutrients and the
hydrogen just stays where the plant puts it.  The soil might get pretty
acidic that way.


> What if the UGF were only one of
> 2 filters, and its flow rate were significantly reduced?

One of my tanks is setup with a UGF circulating about 1 tank volume every
5 hours, or maybe every 24 hours.  Really, its kinda hard to tell.  That
tanks has a fairly coarse substrate and my current feeling is that even
that little circulation is too much for that substrate.

> If I add clay,
> whether laterite, kitty litter, SeaChem Flourite, or just plain red Georgia
> clay, would this not restrict the water's ability to get through?

Absolutely.  An unbroken layer of pure clay will block all water movement.
In a mixture with sand or gravel you will get variable results, depending
mostly on the grain sizes and amounts of each.

> and if I
> used an airdriven Reverse-flow setup, which would allow me to extrapolate flow
> rates using the dye-marker/time-through-the-tube estimation method, could I
> not establish both aerobic and anaeobic sites?

Possibly, but its very difficult to control very low flow rates.  A dosing
pump would probably give you the best handle on it.  I've had trouble with
the dye marker method.  When I tried it I couldn't get good results
because the marker (food dye) was heavier than water and would sink in
standing water.


> But what is the correct flow rate per square inch of <floor>?
> Anyone know what flow rate the Dupla system is striving for with the cables?

You might want to think of this as a residence time, instead of a flow
rate.  You want the circulating water to be resident in the substrate for
a certain minimum amount of time.  Divide the volume of water in the
substrate by your target residence time to find out the flow rate (gallons
divided by hours gives gallons per hour).  Of course this means that you
have to figure out the volume of water in the substrate. For a first
approximation you can use a factor of 0.35; the water volume is 0.35 time
the total volume of the substrate.

When I tried this in the past I aimed for at least 10 minutes of
residence time, but now I think this is too little and that a minimum of
30 minutes might be better, at least for the substrate I used.

Quick example.  I have a 20 gallon tank with a floor area of 1 foot by 2
feet and the substrate is 3 inches (0.25 feet) thick.  My total substrate
volume is 0.5 cubic feet (1X2X0.25) and the water volume in the substrate
is somewhere near 0.175 (0.5X0.35) cubic feet, same as 1.3 gallons.  If I
want a residence time of 30 minutes (0.5 hours), then the flow rate is
only 2.6 gallons per hour (1.3 gallons/0.5 hours).  That's *really* low.

Getting and regulating such a low flow is a big problem (you might try
drip irrigation flow regulators).  It's also a problem that the flow will
tend to concentrate in a few areas, rather than being spread evenly.  I
hope my trumpet snails (those hard working little devils) are up to the
task of keeping the substrate loose and well-mixed and the flows even!

I think that heating cables distribute their energy more evenly so they
might tend to give a more even distribution of flows then you can get from

Roger Miller

In Albuquerque, where there's not a cloud to be seen in the blue, blue