I've tried the split photoperiod, or "siesta" period and found it never had much impact...but I also don't want to totally dissuade folks from experimenting and learning. I always evaluate a method based on Tom Barr's mantra. Does the method help plants grow. The answer
IMO is clearly no. Plants will grow best without having an interrupted photoperiod. Several major changes occur during the light and dark cycles, forcing this change in rhythms doesn't seem logically sound
IMO. If it were the best way to grow plants and keep algae in check all the better aquatic gardeners would be doing it...and so would mother nature. Sure, there are cloudy and rainy days but the light on those days is still quite a bit, certainly magnitudes higher than leaving the tank without lighting.
A few, and I mean a few, folks have reported using a Siesta period has reduced or eliminated algae in their tanks. The most plausible theory in those cases was related to
CO2. In tanks that are
CO2 limited, the siesta period could allow
CO2 levels to build up again during the dark cycle so that overall the
CO2 levels during the shorten lighting period would help the plants grow more than leaving the lights on during a full photoperiod and having
CO2 levels become fully depleted.
It should be noted that Amano mentioned at the AGA conference this year that he is using intense Metal Halide lighting for 3-4 hours during the middle of his photoperiod. He uses low light during the first few hours, then the
MH's, followed by low light. To me, this makes the most logical sense for replicating lighting in the tropics, where most of our plants come from, the problem lies with the cost factor...few have Mr. Amano's budget for a planted tank.
My main point is, try the split photoperiod, if it works great. I'm always in favor of experimentation. I simply want to caution everyone in giving conclusions as to why it does or doesn't work. There are other factors brought into play such as
CO2 and nutrient assimilation. Until I see someone employing the method with repeatable longterm successes I'll personally be skeptical. One thing is certain, algae needs much less light than plants.
