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How much current is enough?

James Purchase wrote:

> Dupla recommended high circulation in The Optimum Aquarium, and to a 
> point it is a vaild argument, but there is such a thing as too much of a
> thing. Dupla recommends between 1-5 turnovers per hour (this is for
> circulation, not filtration). In Aquarium Ecology, a Supplementary
> (a booklet put out by the German manufacturer Tunze), they recommend 1-4
> turnovers per hour in a freshwater tank (and 4 - 10 in a saltwater tank).

Early on I spent some time playing with the amount of current that flows
through my heavily planted 50g.  I bought a bunch of PVC gate valves, some
tubing and cement, and built a contraption that allows me to route as much
or as little of my pump's capacity to the tank - the balance is diverted
back to the sump so only slight additional water head is created at the
pump.  The comfort zone, regardless of the delivery method (spray bar,
nozzle, etc.) seems to be at about 4 water changes per hour as near as I can
guess.  This flow rate allows CO2 to remain in solution but still circulates
the water enough so that no scum forms on the surface (I've got a trickle

> [I wonder what kind of shearing force would be created by using a "spray
> bar" to moderate the output of a powerful pump - I think it might increase
> the problem...]

There are spray bars and spray bars.  One member of our group in San
Francisco has gotten very adept at creating spray bars from landscape
irrigation tubing.  He can punch holes in the tubing in any number of subtle
ways that effect the way the water moves through and exits the bar.  I don't
think one can generalize about shear, but there is another huge advantage to
using a spray bar; you can place it whereever you want it.  My friend has
his spray bar at the water surface in the rear of his tank, with the water
spraying toward the BACK!  He claims the bar itself acts as a sort of
breakwater.  And if I remember correctly, Mr. Barr places his down low in
the back, sending water across the bottom, then up the front of the tank.
Both solutions work - both tanks are beautiful.

michael rubin 
mrubin at visa_com
1(650) 432-4685