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Re: substrate Flows

> Tom Barr wrote:
> 
>> Claus of Tropica mentioned that they tested one tank for optimum flow rates
>> in the substrate and came out with a figure of .49 liters/m^2/day. Not much.
>> Osmosis ain't far behind that.
> 
> That's an interesting value.

I felt so as well. It matched my own observations and notions but I was
still bugged by the RFUG's and their success/contradiction to this.
The cable thing didn't seem to a current issue so much at that point to me.
Too much flow.
BUT they tested only one tank in detail. And that is a difficult leap for a
generalization considering all the variables with a planted tank. Who knows
what secret sauces Claus adds to his tanks:). I take things on faith at
first, try it out and then get more and more critical as I play and find the
limits of these methods.
Then go back and find out the whys.
> 
> Ole Pedersen and Kaj Sand-Jensen (Aquatic Botany 44(1993) p 385-406)
> measured the rate of transport of water from the substrate to the water
> column generated by several different submersed plant species.  In an
> aquarium, water transported upward by the plants will cause an equal
> amount of water to be drawn from the water column down into the
> substrate -- that is, it will cause substrate circulation.  Karen
> Randall pointed that out to this group some time ago.
> 
> Pedersen and San-Jensen's results cover the range from 7 to 143
> microliters per gram plant dry weight per hour.  I'll use a mid-range
> value of 70 microliters/gr/hr for a little calculation.
> 
> I think my 55 gallon tank (0.4 square meters floor area) contains
> something like a kilogram of plant wet weight.  It's reasonable to
> estimate that the plants are about 95% water (about 5% dry weight) so
> the tank would contain about 50 grams of dry plant mass.  That dry
> weight of plants would circulate about 3500 microliters of water per
> hour, of 3.5 milliliters/hour.  Spread out of the 0.4 square meter tank
> area that comes out to 8.75 milliliters/square meter/hour, or 0.21
> liters/square meter/day.
> 
> Gee.  Without any further finagling, that's already at 43% of Claus'
> optimum circulation rate.

It is just one tank though. But this is enlightening none the less and lends
some credence/support to the notions provided here.
> 
> The uncertainties in these estimates are so large that the results can't
> be used for much.  Just look at how the results change if the plants are
> 97% water instead of 95% water!  Despite that, I think they are
> sufficient to demonstrate that plants can provide substrate circulation
> without any additional intervention by the aquarist.

But a general notion or approach perhaps could be explored. I've done my
time with cables. I like were I'm at with the simple plain old flourite/onyx
and plant's roots doing the work. Goes back to the old "let the plants
filter/remove/circulate the tank". Old simple plain advice.
Works great.
Regards, 
Tom Barr