What size aquarium light should I get for my planted tank?

Question

I read that a good rule of thumb is watts for every gallon? I have a 29gallon aquarium, so 29-58 watts of light? I find that a huge difference. I also find it especially difficult to find a light with this wattage to be the correct size for my tank. It seems the higher the wattage, the longer the light. But if I go any smaller in size, the wattage is reduced. I also read that 2 fluorescent lights may be used, but my hood will only house one light. My plants require low-medium light, and low-medium growth rate, ph of 6.0-8.0, so they're generally easy plants to look after. I am experienced keeping Angels, but I can't seem to keep a plant alive! I am trying! There are HUGE benefits with plants and my Angels are happier. Every article I read about lighting for plants contradicts another article I read. One article says that the K rating means nothing, and another article's author swears by using 5000-10000K lights. WHAT do I get? Help!

I mean 1-2 watts for every gallon!

Answer 1

I've grown plants for years and currently own a 29 gallon low tech planted tank with plants considered hard like cambomba growing well. Pretty much lighting wise, the K spectrum does not matter. I've grown plants under cool white bulbs (though these make the fish look bleached out so I don't reccommend it) to more specialize "planted tank bulbs". The plants don't care. My substrate is plain old gravel and I use the Estimative Index for fertilization. I've done everything from pressurized CO2 to natural lighting only but currently prefer the the non CO2 low light method since it involves a lot less pruning.

My current tank (29 gallon) has 3 24" fluorescent bulbs and is densely planted (over 75% of the substrate is planted). It has an assortment of

Valisneria giganthea
Ludwigia repens
Cambomba carolina
Red Cambomba (forgot the scientific name)
Elodea
Anternatheria
Crypt Wentii

I do a 50% water change every 2 weeks followed by a dose of

1/4 teaspoon of Potassium Phosphate (Yes I am adding phosphates to the tank)
1/4 teaspoon of Potassium Nitrate
1 Teaspoon of Potassium Sulfate
1 tablespoon of Magnesium Sulfate (My water has almost no magnesium so this might not be necessary for you)

I also dose 5 mL of Seachem Flourish the following day.

My tank has virtually no algae and the plants are doing excellent.

Go to www.barrreport.com for some more information.

Answer 2

You should be able to find the wattage bulb you need at any GOOD acquarium or pet supply store. Have you thought about a "grow" light. They offer the best of the red & blue hues needed by plants for growth and health. White lights and incandescents only offer a minimum of these hues and are not the best for plants. Various size/wattage grow light bulbs should be available at your local nursery also. So you are not limited to pet stores.

Of course the other thing you need to realize is that no matter what light you get if you have real plants in your acquarium you will need to regulate how much time per day the light is on. Real plants do need about an 8 hour rest period each day.

The other thing you should know is that Angel fish are part of the Chichlid (sick-lid) family and as such are much like the little builders of the acquarium set. They love to move gravel around either by pushing it or by moving it in their mouths. They frequently make pseudo nests even if they are not breeding. The other thing they seem to love to do is to dig up plants. So if you are realizing plants that aren't staying "planted' then your Angels may be the culprets.

When I had angels (along with many other fish) in my 70 gallon tank I used artificial plants. The artificials today are very good in quality and not only look like real, but move like real in the water currents.

Unless you absolutely prefer to have the real plants (instead of the artificials) there is really no "huge" beneficial reason to have them. Yes they absorb some carbon dioxide and do give off oxygen but the vast majority of the oxygen in acquarium water is absorbed at the surface and is not put in the water by plants or air bubbles.

Other than that real plants don't hugely "benefit" the overall health of the acquarium, except to provide some amusement to Chichlids in something to either pull out or dig out of the gravel. If your acquarium was a stagnant pool of water then if would be a different story.

Don't get me wrong, real plants are great and look really nice also. I just got the impression that you feel that real plants are going to vastly benefit the overall health of your acquarium and that isn't truly the case at all as long as you have proper filtration, and circulation of the water by way of the filter and/or some air bubbles.

JMHO. Hope this helps.

Answer 3

Found this from one of my favorite websites, hope it helps!
I've been researching the same recently for my 40gal tank, and i've decided to go for a full-spectrum light fixture. I was told by my LFS that you don't need 2-4 watts of light per gallon if the light being produced is full spectrum. anyhow, check out this article!
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In a planted aquarium, light is the most vital element for healthy plant growth. Plants use light as a source of energy - it is necessary for photosynthesis to occur. Having live plants actually improves water quality. Plants consume fish waste products, generate oxygen, and are the ideal way to obtain an almost self-sufficient ecosystem in which plants and fish happily co-exist.

There are two basic lighting factors which are essential for a luscious aquatic growth. They are 'quantity' and 'quality'. In lighting terms, quantity is usually expressed in watts or more accurately lumens. The higher that wattage the brighter the light - pretty simple. Light 'quality' is a little more complex since it is based on spectral output. The visible light spectrum is made up of different wavelengths or colours of light as can be seen in a rainbow. For best plant growth, the goal is to mimic sunlight as accurately as possible.

To determine the output 'quality' of a light, manufacturers assign two numbers to a light: colour temperature and colour rendering index (CRI). The colour temperature number is used to indicate the colour of light produced by the bulb, and is based on a physics phenomena known as 'black body radiation'. Picture a hot piece of iron in a blacksmith's shop - as it's heated, it starts to glow red, then orange, then yellow and so on - the hotter it gets the more white it's colour appears. Colour temperature is measured in Kelvin (K), and the colour of sunlight at the equator is about 5200 K, unfortunately colour temperature doesn't completely describe the quality of light, this is where the colour rendering index (CRI) comes in to play.

White light is composed of all colours, with each colour being of equal brightness. The CRI indicates who well this equal balance of all colours is matched by your light source. A CRI of 100 is perfect, any number less than this and the light will still appear white, but it may make objects look bluish or reddish for example. A CRI of 70 or more is probably fine for most aquariums.

So, now that all of that technical stuff is out of the way, the question is what does one use for decent planted tank lighting? My recommendation is fluorescent lighting - it's cheap, energy efficient, and will yield exceptional results if your tank is less than 18" deep. The lights should be on for about 10 to 12 hours per day, and you'll need about 2 - 4 watts per gallon with a colour temperature of approximately 5000K and a CRI of 70 or better. Unfortunately, sometimes it's difficult getting a light with this kind of colour spec., so a trick I've found that works quite well is to use two different tubes. You could, for example, use one 'plant light' which is pinkish in colour and has a colour temperature of about 3100K. The second bulb could be a 'daylight' tube which has a colour temp of about 6300K. The result is good plant lighting and a naturally coloured tank.