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Planted Discus Lighting?


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Jun 11, 2019
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Hey guys,

I’m setting up a 4ft aquarium for discus an “light” planting (4-6 plants)

My aquarium has a built in light fixture unit that holds 2 of T5 tubes 39W

The aquarium is L120C x W45C x D75C and is 300L volume

Is the current fixture holding 2 T5s going to be adequate? I’m hoping I can get away with just the 2 T5s?

Also what is going to be the best bulbs to choose, brand an specs etc?

I was thinking 10K bulb on the front of the fixture lighting up the front of the display giving the fish there best colors and putting a 6000K on the rear where most likely the plants will be placed.

I have looked at the aquaone sunlight and the aquaone tropical light for this but I have recently seen Fluval do an 18k and a 6700?

Also I have seen the Zoo Med flora sun and the flora reef sun 50/50, the reef sun being a mixture of 6500k and 420 actinic witch apparently is real good spectrum for Africans and Discus!?!? I didn’t find this 50/50 bulb in T5 only T8

If you can please advise if the 2 T5s is suitable for my application or not and if so what is the best combination of lighting from the T5s for getting the best color out of the discus and also to promote good growth for that the plants need (4-6 plants maybe 8) but not a very heavy loaded planted tank just a few.

Thanks guys!!!


Jan 26, 2008
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Perth, WA
If the tank is 75cm high, T5 globes will not penetrate the water sufficiently to grow plants in the bottom half of the tank. They will provide light to see the fish and for floating plants but nothing growing in the substrate.

Tanks that are 75cm high need two x 200watt spotlights to get the light down to the bottom. You can probably use two x 150 watt spotlights but 200 or 250 watt is better. It also depends on what plants you want to grow. Some low light plants (Java Moss, Java Fern, Cryptocorynes) might be able to survive under the T5s but most won't.

You can buy LED spotlights from most hardware stores. If you get a 150watt spotlight and hang it about 10-12 inches above the tank. Then put your hand beneath the light and just under the surface of the water. If you have a good shadow of your hand on the bottom of the tank, there is sufficient light to penetrate the water. If the 150watt spotlight doesn't create a good shadow, then swap it for a 200watt spotlight.

Don't waste money buying globes with a Kelvin rating higher than 6500K. Globes with 8000K - 10,000K (actinic) are specifically for marine tanks containing corals and have no use in freshwater tanks. They don't even have a reason to be used in marine tanks besides making corals luminesce.

Plants use red and blue light and a daylight globe with a 6500K rating will provide that.


Feb 25, 2009
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I approach this from a different perspective...the fish, rather than the plants.

First comment, a dual T5 fixture holding two 4-foot T5 tubes is way too much light for discus (and most other fish for that matter). You would need a thick layer of substantial floating plants (which you should have anyway for discus as they are dim light fish) but the T5 are very bright. I tried one of these fixtures over my 5-foot 115g tank when the T8 with two 4-foot tubes gave out, and after a week it (the T5) went back. I expected my poor fish to be asking me for sunglasses.

Dual T8 4-foot tubes will be sufficient light for plants if you avoid those requiring high light. Amazon swords will thrive under this, even with floating plants. See the photo attached which was my former 5-foot tank with this light. You could also go with LED, but that could be very expensive and you need to get decent plant light in LED. I have had no good luck with LED so I stay with what I know, T8.


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