Re: Lighting: Duration vs. Intensity

> From: WORKINGSW at aol_com
> >Karla mentioned that it's really 10 hours/day if you count the hour
> >the lights are on in the morning for feeding.  Also, there was not an 
> >algae "problem", just a little more than we like.
> I would like to know more... do you have the lights set for 1 hour in
> the AM for feeding (say, 7-8AM), then rest of the lit-time slanted
> heavily towards evening hours (such as 2pm to 11pm) for viewing while
> you are home to enjoy the fish?  I would like to try a schedule like
> that, but have hesitated for fear of stressing the system.

Ah, an essay question :-).  

We originally had the lights on for 11 continuous hours per day, from
10 am to 9 pm.  This produced great growth but left us "in the dark"
for morning feedings.  There was also occasional periods of algae
growth that the algae eaters couldn't completely control, especially 
red brush algae and green "mat" algae in some of the fine-structure
plants like E. tennellus. 

A year ago (or maybe longer), Uwe Behle in Germany mentioned that
Dennerle recommended turning the lights off for a period in the
afternoon to simulate an "afternoon thunderstorm".  They claimed that 
algae was more sensitive to this disruption than higher order plants 
and would help reduce the amount of algae.  Once we got a copy of
their book and read more about it, we decided to try it. 

All the tanks were switched to a 4 hour morning cycle (7 am to 11 am)
and a 6 hour evening cycle (4 pm to 10 pm).  The tanks with FL lights
were dark during the "thunderstorm" except for very low ambient light.
The tanks with MH lights had the auxilliary FL tubes on during the
dark period (probably not enough light for photosynthesis, but not
completely dark).

After a six month trial, the FL tanks had noticeably lower algae
growth.  Unfortunately, there was also noticeably lower plant growth
among the light loving plants like Rotala and Alternanthera.  As a
matter if fact, we lost our robust stand of R. macrandra and have not,
as yet, been able to find decent starter stock.  The FL tanks are now
on a cycle of 1 hour on in the morning (7-8 am, before work) and 9
hours in the evening (12-9 pm).  All the plants are doing fine (except
for R. macrandra) and there is very little "problem" algae.  

The MH tanks did not have a problem with plant growth nor algae with
the dark period.  Perhaps because of the aux lights, perhaps because
the MH lights are bright enough to fulfil the energy needs even with a
break in the photoperiod. I would guess that the photosynthesis
process needs some time to "get going" and that lag time depends on
the level of energy.  Perhaps the FL lights are just not bright enough
to enable a sufficiently long photosynthesis period or the aux lights
in the MH prevented a total shut-down of photosynthesis.