07-08-2009, 01:37 PM
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In nature tropical fish and plants receive 10 hours of strong daylight and 10 hours of complete darkness, every day of the year. [The other 4 hours are the dawn and dusk period in between, in case you're wondering why 20 hours not 24.] As fish and plants +have been programmed over millions of years to thrive under this arrangement, it makes sense that something that approaches it will be better for the health of both.
It is always best to have the tank lights consistent each day, using a timer is best, and arranged so they are at least on when you are normally there to observe them. Fish can make due with less intense light than plants require to grow, so plants or no plants make a difference in what you set up. There shuld always be room light when the tank light comes on and when it goes out, whether daylight or a lamp is fine; this will be much less stressful on teh fish. There was a post in another thread a day or two ago from someone who had loaches crashing around the tank when the light went on; this is just shock, and should be avoided.
Algae will occur if there is more light and more nutrients than plants can use (in a planted tank). In a non-planted tank, algae is free to utilize all the light and nutrients. The regular weekly partial water change does have an impact by removing some of the nitrates, and algae is always less of a problem in tanks that are regularly maintained. And also in planted tanks.
As mentioned above, the intensity of the light in a fish-only tank can be significantly less than in a planted tank, and this also helps keep the algae from taking control.