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Blue LED light?

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New Member
Mar 18, 2020
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Me again :rolleyes:
Are there benefits to having a blue LED moonlight on in the tank?
My new tank I've set up has a long white LED and a short blue LED. You can have them on singularly or both together.
I presume the "moonlight" is good for nocturnal fish?
Will it have any negative effect on my live plants?

Plant need primarily red and blue light and if they get a bit of green, that also helps them.

Blue lights (moonlights) allow you to view the fish after the normal tank lights go out. However, most fish don't like blue light on its own and many freak out when you first start using them.

If you do want to use a blue light at night, have it on during the day and leave it on for 5-10 minutes after you turn the normal white light off. See how the fish react and if they don't freak out, then you can slowly increase the amount of time you leave the blue light on for.

Do not leave the blue light on all night. If the fish are fine with it, have it on for an hour or two at night and then turn it off so they can have some darkness.

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.
Thank you. Because I can have both on together should I have them both on or just the white light? I could attach pictures of what it is like with both lights on if that would be easier. I just wondered if it has any benefits.

As stated I always open curtains etc when I get up and eventually turn my tank light on around 10am. Then in the evening when I have been sat downstairs with the house light on I turn the tank light off around 10pm and then leave it off until I go to bed and then turn the house light off so I'm glad I've always been doing that right :)

Thanks so much
I don't know what colour light is coming from the straight white part, but if you have blue as well, then run them both and see how the plants and fish go
I agree with what Colin posted (#2).

It would help to know what the "white" light is in terms of spectrum (wavelength). As Colin mentioned, red and blue lights is essential to drive photosynthesis, but red is the more important. If the red is minimal, adding more blue can encourage algae because it cannot benefit the plants. And algae can always make do with any light, whereas higher plants are much more demanding when it comes to light specifics.

Most basic white LED is low in the red and high in the blue, which is why the light has a cool appearance. More red warms the light.

The duration is also important, for fish even more than plants. Use a tier so the light is on for the same period each day. The blue can be used for an hour after the white goes off, but I wouldnot go beyond that. And make sure the tank has several continuous hours of total darkness (no ambient room light).
One of my tanks has a blue moonlight. I set it to come on 15 minutes before the white light goes out and it stays on for another half hour. My tank is fairly dark with floating plants to block out the light - so the only benefit is that I can watch the nocturnal fish feeding after lights out.

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