Mimicking Sundown - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 8 Old 11-28-2012, 08:25 PM Thread Starter
Mimicking Sundown

So I have noticed that when I turn off the aquarium lights my Celebes Rainbow fish freak out, swim erratically and smack themselves into the tank walls in a frenzy. I'm always concerned they're going to hurt themselves.

I figured it must have something to do with the tank going from bright to dark so suddenly so I decided to try something. I first turn on the overhead light for the room my tanks are in before turning off the tank lights, and over a period of about 30-45 seconds, I slowly dim the overhead lights down to dark. Works like a charm! No more upset, stressed out fish at night time. I'm guessing doing this mimics sundown.

Try this if you have fish that also upset easily over the lights being turned off. :)
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post #2 of 8 Old 11-28-2012, 09:00 PM
I've heard of fish going nuts when the lights come on (not off). The story that comes to mind was a fella that had a couple angel fish and when he turned on the lights, they would swim in circles and act messed up. Good bit of advice there, anything to make the tank more like home is probably a good thing. I have no direct experience with something like this though.

Last edited by OhNoFive0; 11-28-2012 at 09:04 PM.
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post #3 of 8 Old 11-29-2012, 01:22 PM
Chesh's Avatar
Good call! Byron has an article posted on how lighting affects fish, and you're right - going from sudden bright to total dark does upset them - same holds true for the reverse. I'm always careful to have the room lights on for 30 minutes or so (for me it's usually longer) before turning the tank lights on or off to give their eyes time to adjust to the change. :)
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post #4 of 8 Old 11-29-2012, 01:26 PM
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Absolutly right.

My tanks turn on between noon to 1 pm, so there is lots of ambient natural light and it does not affect them in the least. But when they shut off about 8 PM it's pitch black, so if I do not have the room lights on they will get stressed.
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post #5 of 8 Old 11-29-2012, 04:15 PM
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The article Byron wrote on fish and lighting is a very interesting read. It contains a lot of good information. One little tidbit that hasn't been mentioned yet is that fish become accustomed to a daily rhythm of when the lights turn on and off. This is their circadian rhythm. Since fish don't have the exact same eye structure mammals do, they actually have to move their eyes to adjust to the light. This isn't something that can be done in an instant like with a pupil, but takes time. I believe I remember hearing about an hour or two. The fish will actually begin this adjustment before the lights turn out in preparation for the expected event. This is why it's best to turn the lights on and off at the same time each day.

Another interesting bit I thought I would add is this: I do the same thing as Geo and have the lights turn on around noon and off around 9p. This works great when I'm there to turn the room lights on at 8.30p, but not so great when I'm not there. For long vacations I'll turn the timers forward to turn on around 8a and off around 4p (when there is still ambient light). When I'll only be gone for a night, I leave a lamp in that room on a timer. I find that's a lot easier than asking another person in the house to mind the lights.


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post #6 of 8 Old 11-29-2012, 07:30 PM
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Hi- having kept Pencil Fish (Eques & Ocellatus ) which startle very easily and often at the top of the water, a few years ago I bought from a store a 14 light LED fixture, slid it into a clear plastic tube , added an anti-roll base to it,placed it on top of the glass tank cover and programmed a timer to turn this fixture on 10 minutes before and slightly after the main tank lights came on, and also 10 minutes slightly before and after the main lights went off. Works like a dream for all the fish, giving them a chance to find cover safely into the plants.
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post #7 of 8 Old 12-01-2012, 05:20 PM
One of the things I have found useful is a small incandescent top. It's a low light and I use it on my 80 gallon so that when it's time for lights on the incandescent goes on first. Shortly after the main light goes on. Later on when it's lights out, the main light goes but the other light stays on. A little while after that that then goes off too.

So far I've had great results with this. I did this for the old 20 gallon set up too.
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post #8 of 8 Old 12-03-2012, 03:22 PM Thread Starter
Originally Posted by Geomancer View Post
Absolutly right.

My tanks turn on between noon to 1 pm, so there is lots of ambient natural light and it does not affect them in the least. But when they shut off about 8 PM it's pitch black, so if I do not have the room lights on they will get stressed.
It's the same here. The lights don't go on until the late morning, so they've already experienced the natural sunrise with the increase of ambient light in the room. It's always been bedtime where they've gotten stressed out.
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