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> From: George Booth <booth at hpmtlgb1_lvld.hp.com>
> Subject: Re: advantages and disadvantages of natural light
> > ...The variability of natural light ...
> > Uwe Behle and George got into a great discussion on this subject in
> > that Krib URL I referenced above. Uwe says in the Aug 9, 93 article
> > that it is suggested by H. J. Krause and Dennerle to have a dark
> > period, either a noon dark period (Dennerle) or an entire dark day
> > once a week (Krause). This is something new for all you folks battling
> > algae to try!!
> It was great until we both decided it didn't work AND it killed off all
> my Rotala macrandra. I was doing a 2 hour dark period (4 on, 2 off, 6
> on). Good theory, bad practice. Sorry.
Do you have any theory on what happened to the R mac George? How did the
plants die? Could your dark period have upset a diurnal rhythym of the
plant? Preserving a low level of lighting during the dark period might
prevent this. That would more closely simulate lighting conditions
during cloudy days. This plant has fine roots which aren't well adapted
to a low redox substrate however that probably wasn't the situation
here. If the overall light budget fell below the compensation threshold
for Rotala macrandra, the plant could not produce sufficient sugars or
energy reserves to sustain growth. This plant does require strong
>From your comment, I gather that you weren't able to observe a
difference in algae growth? As mentioned in the Krib article, green
unicellular algae would be the most susceptible to this treatment.
Filamentous algaes survive dark periods quite well. What types of algae
were you testing?