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I've got a fish-only 29 gallon freshwater tank and picked up a new bulb. The bulb I got is a 4200K bulb and is a lot more yellow than the last bulb that was in there.

Not sure if I like it, but I'm wondering if this bulb will not induce algae growth as much since it's not designed for planted aquariums... or if I should get one of the 18000K bulbs because I like the coloring better.

Thanks for any help.

~Michael

Algae will grow under any light even incandescents which are nearly all yellow light to actinics which are all blue light. The spectrum has much less affect on algae than it does on plants. If you have no plants then spectrum doesn't really matter beyond your preference for how the tank looks.

Hi,
To best see the fish, and not be bothered by "dingy"
appearing light, you would want a "white" light.
18,000 is way too bright and is tending towards the
blue end of the spectrum. Bulbs that high in "K" rating
are more designed for Saltwater Reef tanks where that
harsh a light is necessary for the invertebrates in the
tank. Lighting with a 10-18,000K bulb is very harsh.
Many fish feel "exposed" to predators under
conditions like that and need shaded areas for their
comfort.

Frankly, I think you would do better with a bulb in the
6700K - 8800K range, they are white, and give a true
color rendering (CRI) of what the fish actually look like.

Here is an interesting site that describes the "K" rating
visually.
http://www.1000bulbs.com/page.php?s=KelvinTempExplained

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Thanks.

I didn't even think about it but the CFL bulbs in my living room & loft are 6500K, which the relative lighting color probably makes the aquarium look even more yellow. The bulb is a SunGlo 4200K. They have a LifeGlo which is a 6700K, so I'll probably bring it back and swap it for that.

Been a long time since I've set up a new (or re-newed) tank

~Michael