Light Timing - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 4 Old 09-11-2011, 08:34 AM Thread Starter
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Light Timing

I have a 72g that has T5 lights. I'm in the process of cycling the tank and it was recommended that I run the lights for 6 hours a day.. When I plant it next week I know I will need to increase the time period to about 8-10 hours.

Can I split the time??... Like on for 2 hours in the morning 7am-9am and then on for 4 hours in the evening 5pm to 9pm.. Then increase the afternoon time when planted.

I would like to view the tank in the mornings and then again in the evenings..

Thanks for any input..

Capt Roy

"If it doesn't work, read the directions. If it still doesn't work, follow them!!"
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post #2 of 4 Old 09-11-2011, 10:35 AM
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There are people who do this, and its said to help combat algae growth.

The only problem you might have is when you add fish, I'd personally never do it this way because its going to drive the fish crazy.

I had this issue where I was having to turn mine on in the mornings before I left for work, and then by the time I got off Id have to turn them right off since theyd been running for 10 hours.

I finally decided Id have more time to look at them at night, so I got a timer and have the lights turn on around 1 and go off at 10pm. This way I have plenty of viewing time in the evenings when I get off work
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post #3 of 4 Old 09-11-2011, 11:34 AM
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First off, welcome to Tropical Fish Keeping forum.

Now to the light. T5 presumably means HO (high output), which is considerably more intense light that regular T8. You haven't mentioned the number of tubes or their size, so I can't provide any guidelines; nor have you mentioned CO2 diffusion, and this has a considerable impact. So for the moment I'll leave the matter of total photo-period (duration) until I know these factors.

With respect to the "siesta" approach as it is commonly referred to, I believe you will need to adjust the "on" periods a bit. Plants need sufficient time to use the available nutrients in photosynthesis. Most sources advocating this method suggest 4-5 hours on, 2-3 off, then 4-5 on. Here again, the nutrient availability has a significant impact, particularly CO2, so knowing that will help; without sufficient nutrients available, the plants cannot use the light, and algae will take advantage.

There is also the matter of the fish. Plants can adjust to a "siesta" system, that we know. But the impact on fish is as yet not fully understood. I always address increasing algae issues by reducing the photo-period, and I have kept it continual every 24 hours solely because I am not certain of what long-term effect a siesta method might have on the fish. Biologically fish expect 10 hours of daylight and 10 hours of complete darkness during each 24-hour period [dawn and dusk being the other 4 hours obviously]. There are ramifications to this that I won't go into here. I have searched around, but so far not found any source that specifically addresses the issue. The ambient room light is of paramount importance. Most aquarium fish are forest fish that occur in dimly-lit streams with minimal or even no direct sunlight. Provided the ambient light is sufficient to still be "day" to the fish, the tank lighting could be considered direct sunlight between clouds or shading by forest canopy or something. This should pose no issues, but I am only guessing.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #4 of 4 Old 09-11-2011, 10:08 PM
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A simple solution for the non driving fish crazy, if you have some left over T8's from days gone by. Run those for the extra hours. It'll give the tank light, but not effect the plants. Lights dim enough not to cause algae havok but i figure good enough so that the fish don't get too annoyed. What I am doing currently in a 55 gallon is running two T8's for four hours a day then my T5HO's for 6 hours a day, giving them 10 hours of day light but only tempting the algae with 6 hours of High output light rather than the full 10.
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