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RE UV wattage question



If you have fish in the planted tank, do you think that 50% water
changes weekly could be more stressful than lesser changes?  Do you
recommend 50% weekly changes as a temporary or a permanent measure?

Do you recommend a 15 watt UV for any size tank?  If so, why 15 watts
rather than some other size?  It seems that, since the lethality is a
direct function of total effective exposure, which is a function of
lamp intensity, and total exposure time, some cases require larger and
others smaller lamps?  Of course, if the exposure rate is above the
lethal minimum for algae, and all of the water makes it through the UV
lamp during the period that it is turned ON, the lamp will be
effective.  Based on the charts that I have seen for single pass
lethality, 15 Watts is probably overkill for most tanks using a small
water pump, say, a filter output.  This seems all the more true if the
lamp is being left on for a day or two, so that all of the tank water
cycles through the lamp many times, given that repeated exposures are
lethal at somewhat lower intensities and durations than single pass
exposures.

The difference in price between 8, 15, and 30 watts is considerable. 
If a person had only tanks smaller than 60 gallons, an 8 watt lamp
might be more than adequate and less expensive to purchase and
maintain.

 
Scott

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