UV light for Plants in Tank

sometimes UV is used to treat bacterial and communicable fish diseases i think
These UV lights are inside a casing (often a filter but there are stand alone UV sterilisers), and the water passes through the casing next to the UV light. UV sterilisers are never used in a fish tank outside a casing.
 
I have one of these in 24w (brilliant for keeping green water, floating algae and even the occasional bacterial bloom at bay...I use mine maybe 48 hours per month, if at all. It lurks in the corner of the aquarium ready and waiting should the need arise)


But I suspect that the OP means one of these


Two different beasts entirely but easily muddled due to the shade of blue often given off by the Fluval plant spectrum lighting that looks more violet than blue depending on the setting used

Ideally you do not want blue/violet on all the time. I don't have the Fluval but I do have a Nicrew MCR LED that works in the same way....first thing in the morning and last thing before lights out, I go bluey just to ease the fish into wake up mode or time for bed mode. I do have live plants in my aquarium which despite my track record are not dying yet (actually doing anything but dying at the moment). They seem unbothered by the blue lighting that is on for about 45 minutes each end of the 7 hour aquarium day.

I will add that I use blue aquarium lighting in my kitchen as overnight security lighting - it is attached to the wall underneath the kitchen wall units - and my parlour palms that had been close to death have perked up no end since I started using the blue lights all night in the kitchen

I absolutely do not recommend using any lighting (blue or otherwise) all night in the aquarium. Fish and plants need sleeping time and total darkness...just like every living thing.
 
If you have done any snorkeling or scuba diving you know that the light becomes all blue below about 10 ft. The other colors are all absorbed. Blue lighting.bulbs for reef tanks is often referred to as "actinic lighting."


"Corals don’t need a white light to grow in your reef tank. Instead, they need blue light to grow healthily. White light is more useful to humans, as it helps them ‘see’ the corals in the reef tank better.

Corals Need Light To Grow​

Corals in reef tanks are photosynthetic, meaning they rely on light, such as blue light, to produce the food they need.

Zooxanthellae, the algae-like beings that live on coral polyps, contain chlorophyll. As such, they need to utilize light to create sugar, the coral’s main source of energy. In fact, zooxanthellae help provide 80–85% of the nourishment that the coral needs.

As an appreciation for the algae’s nutritional gifts, the coral provides them with the shelter and carbon dioxide they need.

What Kind of Light Do Corals Need?​


The blue light spectrum, not white, is what corals need for optimum growth. It helps stimulate coral reef calcification, which is the primary measure of growth. In this process, the corals lay down the foundations of their calcium-rich skeletons.

According to a study, blue light also helps increase the number of Zooxanthellae in corals. It helps boost Chlorophyll A levels in these algae as well.

For one, Chlorophyll A can only absorb wavelengths ranging from 440 nm to 675 nm. Blue light, with its shorter waves, only has a wavelength of 450 to 495 nm. Indeed, it’s a perfect fit for the photosynthetic needs of Chlorophyll A.

Blue light does more than promote coral growth, though. It can also help influence the coral’s pigmentation, as it boosts the production of chromoproteins.

These give the corals their trademark hues. That’s why when you use blue light in your tank, you’ll see fluorescent colors you won’t see in the traditional full-spectrum lighting."
 
These UV lights are inside a casing (often a filter but there are stand alone UV sterilisers), and the water passes through the casing next to the UV light. UV sterilisers are never used in a fish tank outside a casing.
ah i see
the exposed light would be dangerous
 
Can you post a photo of the light including any writing on it.

Marine tanks often have blue lights. Some LEDs marketed for freshwater have an option for only blue or mixed blue and white. This is not the same as UV light.

If it really is UV, you shouldn't look at it as UV is not good for eyes.
Our light from Fluval tanks
 

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Just blue is OK for half to an hour just before the main lights turn on and after they turn off, but that's all. From what other members have said in different threads, too much blue encourages algae. And even just blue should not be on all night as fish need a period of several hours total darkness.
 

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