Will using moon lights in low tech tanks cause algae? - The Planted Tank Forum
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post #1 of 11 (permalink) Old 08-03-2020, 08:37 PM Thread Starter
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Will using moon lights in low tech tanks cause algae?

My tank is a walstad tank and just recently, I got a new LED light. When it's on during the day, I don't use any blue in my settings but I would like to use it for about 30 minutes to an hour after the lights go out for the night. I would only have it set to, at the most 10%.

Could using the moon lights(blue) for only an hour tops cause algae? I've heard many people say to avoid using blue lights in low tech tanks.

Thanks.
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post #2 of 11 (permalink) Old 08-12-2020, 07:03 PM
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Blue light is your plant's best friend. White light is for you, not so much them. In my opinion, the best approach with adjustable led fixtures is to find a pleasing color ratio using as much blue and red as possible. I like to use green as well but the plants don't care about it. Then dim/increase the entire fixture to the appropriate level while keeping the same ratio.


Blue light will encourage plant growth. All kinds of plants, including algae. This is where you balance light intensity, carbon availability, and ferts to keep algae away. Moonlights for a few hours shouldn't be a problem.
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75g...medium tech...?
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post #3 of 11 (permalink) Old 09-12-2020, 09:36 PM Thread Starter
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Originally Posted by Crazylegs78 View Post
Blue light is your plant's best friend. White light is for you, not so much them. In my opinion, the best approach with adjustable led fixtures is to find a pleasing color ratio using as much blue and red as possible. I like to use green as well but the plants don't care about it. Then dim/increase the entire fixture to the appropriate level while keeping the same ratio.


Blue light will encourage plant growth. All kinds of plants, including algae. This is where you balance light intensity, carbon availability, and ferts to keep algae away. Moonlights for a few hours shouldn't be a problem.
Good to know.

I do have another question for you, if you don't mind.

You mentioned that plants like reds and blues but you also mentioned green. How would a person set up their lights if most of the LEDs in the fixture are whites? I use the Fluval Plant 3.0 and the colours to adjust are pink(red), blue, cold white, pure white, and warm white. From the different settings I've seen people use, they always have the blue the lowest and the whites and pink much higher. Shouldn't the blue be up there with the pink instead of being much lower in intensity?
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post #4 of 11 (permalink) Old 09-13-2020, 02:20 PM
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Hi @ MintyFresh

Have a Google for "PAR vs PUR" and I think this might help answer some of your questions. Here's a good starting point:
https://answers.seneye.com/index.php...AR_%26_PUR_%3F

Plants mostly reflect green light, that's why they look, err.... green!

You could have the brightest green light shining down on your plants and they would look very green, but they're not really going to grow. They need red and blue light, which is why you see some hydroponic grow lights having just red and blue LEDS (they typically look pink or purple), the logic being that green light is just wasted on the plants, so use the electricity to give the plants the blue and/or red light they need. Flowering and fruiting plants need more red light, for foliage growth (leafy veg for example) they need more blue.

But an aquarium lit with only red and/or blue light would look ghastly! In my hydroponics I use warm white "full spectrum" grow lights with some extra red and blue boosts because I want to be able to see in the same room to see if the plants are healthy etc. Ok the green light is wasted on the plants, but not on my eye's viewing the plants.

Exact same logic for tanks. All these colour tuning options are there because they can be with LED tech, not because they actually need to be! Find a light "colour" that makes your tank look the way you want it to during the day. Some mix of cool and warm white LEDs to get the morning, midday, afternoon feeling you want. Add in some extra red if you have red plants or fish and want to make them really pop out, but remember this is only for your benefit really - it won't make much difference to the plants or fish. White light (warm or cold) has everything the plants need to grow and for you to look at them.

A dim blue "moon" light for an hour or two of an evening is not going to make any difference to any sort of plant (or algae) growth.

These options are really only there for you to play with and enjoy (some might say gimmickry). They will make very little difference to the tank life. If you get algae, it's almost certainly not because of an hour or two of blue dim moonlight each night!

I short, set the light colour to whatever you like the look of. It's the intensity that will make the difference to the plant life, not the colour.

Hope this helps, regards, James
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post #5 of 11 (permalink) Old 09-13-2020, 02:36 PM Thread Starter
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Hi @ MintyFresh

Have a Google for "PAR vs PUR" and I think this might help answer some of your questions. Here's a good starting point:
https://answers.seneye.com/index.php...AR_%26_PUR_%3F

Plants mostly reflect green light, that's why they look, err.... green!

You could have the brightest green light shining down on your plants and they would look very green, but they're not really going to grow. They need red and blue light, which is why you see some hydroponic grow lights having just red and blue LEDS (they typically look pink or purple), the logic being that green light is just wasted on the plants, so use the electricity to give the plants the blue and/or red light they need. Flowering and fruiting plants need more red light, for foliage growth (leafy veg for example) they need more blue.

But an aquarium lit with only red and/or blue light would look ghastly! In my hydroponics I use warm white "full spectrum" grow lights with some extra red and blue boosts because I want to be able to see in the same room to see if the plants are healthy etc. Ok the green light is wasted on the plants, but not on my eye's viewing the plants.

Exact same logic for tanks. All these colour tuning options are there because they can be with LED tech, not because they actually need to be! Find a light "colour" that makes your tank look the way you want it to during the day. Some mix of cool and warm white LEDs to get the morning, midday, afternoon feeling you want. Add in some extra red if you have red plants or fish and want to make them really pop out, but remember this is only for your benefit really - it won't make much difference to the plants or fish. White light (warm or cold) has everything the plants need to grow and for you to look at them.

A dim blue "moon" light for an hour or two of an evening is not going to make any difference to any sort of plant (or algae) growth.

These options are really only there for you to play with and enjoy (some might say gimmickry). They will make very little difference to the tank life. If you get algae, it's almost certainly not because of an hour or two of blue dim moonlight each night!

I short, set the light colour to whatever you like the look of. It's the intensity that will make the difference to the plant life, not the colour.

Hope this helps, regards, James
Thank you so much, James! This has been very helpful.

My main concern with the blue light at night or just increasing it more during the day, is because of algae. A few months ago, I had a light dusting of GDA. It's cleared up since then but I'm always concerned that it might come back. I had read that algae tends to favour blue light which is what prompted me to ask about this.
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post #6 of 11 (permalink) Old 09-13-2020, 07:08 PM
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As others have said; plants need blue light to fulfill their potential. However, if you are happy with your plants as they are, you might not be happy if you make any type of change, which includes things other than light. My concern is that, if you are starving your plants for blue light, they may not be strong enough to withstand a change in anything, e.g.; if they suddenly don’t get enough of a nutrient, they may go into an unrecoverable tailspin. Additionally, strong plants act to deter algae.

If you do decide to ramp-up your blue, make sure that all of your nutrient bases are covered and that your photoperiod and total intensity (PAR) are tuned to a low-tech setup.

Algae will take advantage when plants falter. It is better to have good and robust plant health than to try to starve algae. You simply cannot starve algae in a planted tank. You have to do other things to cause it’s deterrence. Your GDA was probably not a result of your blue light. I would tend more toward organics (cleaning issue) or a nutrient imbalance, if it was not a new setup.

If you are confident of a healthy plant mass, then using a little blue-only (assuming that you are going for that aesthetic look) won’t disturb anything. If it does, I think you have to re-think your overall light balance approach.
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post #7 of 11 (permalink) Old 09-13-2020, 08:32 PM
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"You could have the brightest green light shining down on your plants and they would look very green, but they're not really going to grow. They need red and blue light, which is why you see some hydroponic grow lights having just red and blue LEDS"

"I short, set the light colour to whatever you like the look of. It's the intensity that will make the difference to the plant life, not the colour."

Hi James, just want to double check what you meant bcs I read this as possibly contradictory. Are you meaning in the last paragraph that aquarium plant lights are going to have all the spectrum plants need, therefore the color setting is just for our eyes, and intensity is what matters?
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post #8 of 11 (permalink) Old 09-15-2020, 12:50 PM
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Hi @novato,

Sorry, I see the slight contradiction there. But basically just set the lights to what you like the look of. Assuming that you don't have some very peculiar taste in how you like plants to look, then this is going to be somewhere on the "white" spectrum. I'm suggesting that the difference between warm white (orangey tint) and cool white (bluish tint) is pretty small from the plants perspective - it's all just white with a bit extra blue or red thrown in. The choice or warm or cool white is primarily your visual preference. Depends upon the colour of your fish and plants too; adding in extra red will make red plants / shrimp / fish 'pop' more, but it could also start to diminish the vibrancy of bright green foliage. Play around with the settings, see what you like and what brings out the colours in your plants and livestock best. Get really fancy and change the colour temperature throughout the day to cool midday sun, warm 'golden hour' afternoon sun etc if you like, but this is only for your entertainment, pleasure and satisfaction (the tank won't care less!).

When you have the colour set the way you want, then adjust the intensity of the light to suit the plants / CO2 / fert's etc. LED lights are pretty powerful so you most likely won't need to be running flat out at 100% anyway (I run my Kessil at about 40% max, but my tank is shallow). The beauty of LEDs is that colour temp and light intensity are largely independent of each other, so you can set the colour to your taste and the intensity to what the plants need.

Does that make sense? If you need something to add to your Christmas list, check out the Seneye Reef device. It has a PAR / PUR / colour spectrum function which is incredibly cool! I bought one to tune the lights in my hydroponics system, but also great for setting the light intensity in aquariums (the other functions don't really work in low KH freshwater, but the light meter functions are worth the cost alone!). This is how I was able to dial my Kessil back to only 40% as opposed to the 60-70% max I thought I needed by sight.

Kind regards, James =)


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post #9 of 11 (permalink) Old 09-15-2020, 05:23 PM
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I have used moon lights on a low tech tank for a long time and have never seen any relation to algae. I can't imagine there is enough light energy. I'm sure some minuscule amount of algae could grow, that perhaps is able to use light at the wavelength(s) the moon light produces. But given the extremely low output of a moon light, that growth would be unnoticeable.

Last edited by ahem; 09-15-2020 at 05:23 PM. Reason: correct spelling grow --> growth
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post #10 of 11 (permalink) Old 10-12-2020, 03:41 PM
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Interesting!

It does not promote algae growth and will only help plants a little, if a lot is used. www.landclearingofwa.com/
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post #11 of 11 (permalink) Old 10-19-2020, 02:26 AM
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To more directly answer the question - NO.

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