Room lights stressing fish??

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Aquarium Advice Newbie
Mar 27, 2023
Hi I am pretty new to this. I have a planted 9 gallon tank stocked with guppies and tetras. I leave my aquarium lights on for about 8 hours a day. Recently purchased a timer to make things easier. I have the tank in the living room. My question is, will my room light stress my fish after their tank light has gone out? So I am not always working the same shift patterns and so will very often come home after the tank light has gone out so I am having to come home and put rooms lights on in a previously darkened room. If the fish have settled down for the night or are resting, will this not disturb their sleep patterns and/or stress them longterm? I have noticed sometimes when i do this that a couple of the tetras start to dart around the tank for a few minutes but usually calm down. I try to use a softer light such as a lamp rather than the main room light. Am i overthinking things or could this be an issue? Any help would be appreciated

Thank you,
No. It will be fine. In fact its a good idea to have the room lights come on (or get natural daylight in the room) a little before your tank light comes on, and turn the room lights off a little bit after the tank light goes out. This is so the fish arent startled by the intense light above suddenly coming on or going off.
If the tetras dart about when you turn the room light on, then it is stressing them. I would get a desk lamp and have it in the room but on the opposite side of the room to the aquarium. Have it on a timer so it comes on 10 minutes before the tank light goes out and it can stay on until you get home and go to bed. This will allow the fish some light and they won't be stressed out when the room goes from complete dark to bright light.


Stress from tank lights coming on when the room is dark can be an issue. Fish don't have eyelids and don't tolerate going from complete dark to bright light (or vice versa) instantly.

In the morning open the curtains or turn the room light on at least 30 minutes (or more) before turning the tank light on. This will reduce the stress on the fish and they won't go from a dark tank to a bright tank instantly.

At night turn the room light on and then turn the tank light off. Wait at least 30 minutes (or more) before turning the room light out. This allows the fish to settle down for the night instead of going from a brightly lit tank to complete darkness instantly.

Try to have the lights on at the same time each day. Use a timer if possible.

If you don't have live plants in the tank, you only need the light on for a few hours in the evening. You might turn them on at 4 or 5pm and off at 9pm.

If you do have live plants in the tank, you can have the lights on for 8-16 hours a day but the fish and plants need 8 hours of darkness to rest. Most people with live plants in their aquarium will have the lights on for 8-12 hours a day.


Most aquarium plants like a bit of light and if you only have the light on for a couple of hours a day, they struggle. If the light doesn't have a high enough wattage they also struggle. Try having the tank lights on for 10-12 hours a day.

If you get lots of green algae then reduce the light by an hour a day and monitor the algae over the next 2 weeks.
If you don't get any green algae on the glass then increase the lighting period by an hour and monitor it.
If you get a small amount of algae then the lighting time is about right.

Some plants will close their leaves up when they have had sufficient light. Ambulia, Hygrophilas and a few others close their top set of leaves first, then the next set and so on down the stem. When you see this happening, wait an hour after the leaves have closed up against the stem and then turn lights off.

Plant lights should have equal amount of red and blue light and a bit less green light.
Hi Jack!! Welcome!

Guppies are hard to take care of compared to tetras. Guppies tend to be inbred and already come with many issues so be careful that it isn’t a disease but it is just the lights. As someone who have owned guppies and tetras, they do not mind. I often do work with their lights off and my room light on. They will sleep regardless. If you see that they are stressed then try to dim your lights or keep them off during their sleep time.

:) Happy fishing!
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