New to Plants Advice - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 3 Old 02-10-2012, 03:11 PM Thread Starter
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New to Plants Advice


I just purchased a 15 gallon tank that is 2 weeks old with a few plants. I am using a 15 watt 18" long 5000 k daylight light.

Is that enough light? I have read between 1 watt and 2 watts per gallon but that was the strongest light they had at the petstore. Can I leave the light on for 12 hours to add more light?

Thank you.
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post #2 of 3 Old 02-10-2012, 03:30 PM
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pet store light are expensive. i buy online from lowes or home depot way cheaper for bulbs.
also that is enough light tho.
you could go brighter to speed growth, but will risk algae blooms with xtra uneeded light
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post #3 of 3 Old 02-10-2012, 06:03 PM
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I agree, that is sufficient light intensity (with a good full spectrum or daylight tube as you say you have) for the majority of plants in a 15g tank.

Just so you know, watts is not a reliable guide any longer, as so many new types of fluorescent lighting tubes are now being developed that are energy efficient. Watts is just the measurement of energy that it takes for the tube or bulb to produce the light, so a better-made more energy-efficient tube can use fewer watts but still produce comparable light to another tube. As an example, a Compact Fluorescent Bulb of 10w will produce light intensity comparable to the old 25w incandescent bulb. So you can see how "watts per gallon" and such becomes rather meaningless, unless you know exactly what the tube/bulb emits in terms of actual light.

And longer duration does not compensate for less intensity (brightness), just so you know. Plants grow by photosynthesis, and to do this they need sufficient light (intensity) along with 17 nutrients. With respect to just the light, if it is too weak for them to photosynthesize, they cannot, no matter what the duration. But algae will take advantage as it can use any light. Assuming the intensity is sufficient (as yours is) the duration should always be in balance with available nutrients, and light should be the limiting factor to avoid algae issues.

And, welcome to Tropical Fish Keeping forum.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

Last edited by Byron; 02-10-2012 at 06:05 PM.
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