Frequent Aquarium Questions

• I recently changed the bulb on my 36" hood to a T12 Sunglo, I found the original bulb was a T8. It works, but is this safe? Will it wear out the ballasts sooner?
  
  
• What is the appropriate wattage range for a fluorescent light bulb in a 10 gallon tank? The tank is now housing goldfish.
  
  
• Which is better for goldfish in a 10 gallon tank, a glass canopy with an additional fluorescent light or a full hood such as AllGlass or Perfecto?
  
  
• How long should the lights be on in my aquarium?
  
  
• Aquarium bulbs seem very expensive. Can't I use cool white fluorescent bulbs from the hardware store?
  
  
• What does Kelvin temperature refer to in aquarium light terminology?
  
  
• What spectrum of light is right for my aquarium?
  
  
• How much light do I need for my live reef aquarium?
  
  
• What is the difference between a color rendering index rating and the wave length rating in nanometers? can one be converted to the other? and how do they both apply to the aquarium community?
  
  
• The plants in my small (5 gal)aquarium are turning yellow. The aquarium has been running for about 3 weeks. The temperature is 78, pH is 6.8, and the tank contains 3 Angelfish. What have I done wrong?
  
  

• I recently changed the bulb on my 36" hood to a T12 Sunglo, I found the original bulb was a T8. It works, but is this safe? Will it wear out the ballasts sooner?
  
  T12 (1-1/2" diameter) lamps will work in fixtures that were originally equipped with T8 (1" diameter) lamps with no problems. The only difficulty encountered is that the thicker lamps may be harder to remove and replace in some fixtures that are very narrow such as in standard hoods and strip-lights.
  
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• What is the appropriate wattage range for a fluorescent light bulb in a 10 gallon tank? The tank is now housing goldfish.
  
  That tank will take a 20" strip light or a 20" full hood. In both of those fixtures, yoyu can only use a 15 Watt, 18" fluorescent lamp. That is a suitable size though, so you should do fine.
  
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• Which is better for goldfish in a 10 gallon tank, a glass canopy with an additional fluorescent light or a full hood such as AllGlass or Perfecto?
  
  For goldfish, either would be suitable. However, if you plan on later converting the tank to tropical fish and live plants, or setting up a nano-reef aquarium, you would be better served buying the glass canopy/strip light configuration. BTW: Regardless of which you choose, make sure the canopy or full-hood is made by the manufacturer of your aquarium, as sizes are proprietary.
  
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• How long should the lights be on in my aquarium?
  
  To answer this question, we need to know what type of an aquarium you have, the lighting you're using, and whether the tank receives any direct sunlight. The wrong answer here could create a bad algae problem or help to destroy photosynthetic organisms.
  A generic answer is six to twelve hours a day. If you have a fish-only aquarium, either fresh or saltwater, six to eight hours a day is fine. If however, you have a freshwater live-plant or a marine live-reef aquarium, ten to twelve hours a day works best depending on the lighting type used.
  The length of daylight each day, and the length of time aquarium lights are on, is called "photoperiod." A constant photo-period benefits almost all fish and invertebrates. The lights should turn on and go off at roughly the same time each day. The only exception to this is in some specialized lighting situations where the photo-period shortens and lengthens via variable automatic timers, to simulate seasonal changes for specialized husbandry applications or state-of-the-art reef tanks. We recommend the use of a light timer to control the lighting on all aquariums.
  
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• Aquarium bulbs seem very expensive. Can't I use cool white fluorescent bulbs from the hardware store?
  
  Please don't unless you absolutely have to! Many algae, plants and animals, including humans as well as many fish and sessile invertebrates, require all or part of the specific spectrum of light the sun produces, to manufacture, or to metabolize important nutrients. Many fluorescent aquarium bulbs are designed to simulate part or all of the spectra produced by the sun. Some aquarium bulbs produce a spectrum designed primarily to enhance the colors of fish. While cool-white bulbs will illuminate the aquarium just fine, they are not designed to produce the correct spectrum to promote health in fish, plants, algae or invertebrates. Not to mention that if you do use cool-white bulbs, you'll see your fish in a whole new dull-and-drab-colors-all-washed-out kind of way. You may also experience rapid growth of funky-looking brown algae in your aquarium.
  
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• What does Kelvin temperature refer to in aquarium light terminology?
  
  The Kelvin temperature scale is frequently used in science because it describes absolute temperatures, and is only indirectly related to the Kelvin color temperature scale used by the light bulb industry to describe the spectrum of light that different light bulbs produce.
  Fluorescent bulbs are coated inside by rare-earth phosphors and filled with mercury vapors. Low-voltage electricity is discharged at the ends of the bulb and conducted by the mercury, which "excites" the molecules in the phosphors, and causes them to glow brightly or fluoresce. Over time, this process takes its toll on the phosphors and they begin to degrade, and eventually they burn out. Different phosphors fluoresce with different colors of light.
  The Kelvin color temperature scale is used to describe different colors, or spectra of light, using a scale based on the spectrum of light produced by the sun at it's peak or zenith (12:00 Noon), on a clear day. This reference color temperature is 5500ºK. Bulbs that are designed to produce light with a color temperature of 5500ºK are called daylight bulbs, and produce a full-spectrum of light. Bulbs that produce color-temperatures lower than 5500ºK, produce more red to orange light in their spectrum. Bulbs that produce color-temperatures higher than 5500ºK produce more blue to violet light in their spectrum. Lighting to enhance the colors of fish and aid in the growth of freshwater plants is usually rated at 4500ºK to 5000ºK, whereas lighting used to stimulate photosynthesis in reef aquariums is usually rated at 5000ºK to 7500ºK. Newer bulbs on the market for reef and planted tanks produce color temperatures of 10,000ºK and even 20,000ºK. We've used bulbs producing 6500ºK, supplemented by bulbs producing 7100ºK to 7500ºK (more for appearance) on our client's reef and planted aquariums with excellent results.
  
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• What spectrum of light is right for my aquarium?
  
  This depends on the type of aquarium you keep. If you have a fish-only aquarium, either freshwater or marine, you may want to use a normal fluorescent aquarium bulb, which produces a slightly red, warm color that enhances the colors of the fish. Lighting to enhance the colors of fish and grow freshwater plants is usually rated at 4500ºK to 5000ºK, which brings out the colors of the fish but results in less algae growth. If, however, you have a marine reef tank, we recommend using bulbs rated at a color temperature of 5000ºK to 7000ºK, which stimulates photosynthesis in algae and the symbiotic algae that live in the outer integument or calcareous matrix of many sessile invertebrates called zooxanthellae.
  
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• How much light do I need for my live reef aquarium?
  
  The good old generic rule-of-thumb is 7 to 10 watts per gallon of reef aquarium, depending on the surface area and depth of the aquarium. This rule still works for some common aquarium sizes, but it is imperfect for several reasons.
  A watt is a unit of how much power a bulb produces. Two different bulbs producing the same wattage may not produce the same amount (intensity) of light. The more surface area an aquarium has, the more light will be required. Water absorbs and scatters light, so light penetration also decreases as a function of water depth.
  If a reef tank does not get enough light, corals and algae will close and slowly wither away. If there is too much light (not a common problem), the aquarium will be overcome by algae, and corals may get "bleached" out and die.
  If you want to calculate the ideal light wattage required for your reef aquarium, we suggest you read one of the excellent books on our reef aquaria books page. Here, we would rather tell you what has worked for us and allow you to get scientific about the complex subject of light intensity requirements for reef tanks on your own. These recommendations are all based on bulbs used per two feet² of tank surface area in aquariums no more than 24" in height:

175 watt, 6500°K metal halide & 1 - 55 watt, 7100°K Power Compact® bulb
175 watt, 6500°K metal halide & 1 - 40 watt, 7100°K fluorescent bulb
We highly recommend some form of metal halide lighting system for reef tanks. We have also had great results with systems that use only Power Compact® bulbs, but these will not support many of the hard corals and certain other sessile invertebrates that have high-light requirements. Remember that it is your responsibility to make sure you meet the life-support requirements of the aquatic animals you want, BEFORE you go out and buy them.

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• What is the difference between a color rendering index rating and the wave length rating in nanometers? can one be converted to the other? and how do they both apply to the aquarium community?
  
  We actually have to discuss three factors here, not two. Those are Light Spectrum (wavelength), CCT (Correlated Color Temperature), and CRI (Color Rendering Index). We will only deal with visible light, as things start getting really complicated at either far end of the spectrum, and I will probably confuse you enough with this explanation. Here's the simple (and slightly inaccurate) explanations: Wavelength is the actual colors in the spectrum that are produced by a light source, measured in percent of nanometers over the spectral scale. Wavelength specifications are the only absolute measurement of a lamp's color output. Color Temperature is a relative measurement of the perceived color (to the human eye) of a light source, measured in degrees Kelvin. Although based on and related to the spectral wavelengths of a light souce, there is no way to convert one to another, as a lamp that produces many light wavelength peaks over a wide nanometer range in the spectrum will have a similar color temperature to one that produces only specific spikes in the same nanometer range. Most lamps tend to range from 4000K to 20,000K, with 4000K looking more red and warm, and 20,000K looking more cool and blue. A 7100K lamp for example, is not necessarily a true Actinic lamp. True Actinic lamps produce most of their light in a very specific wavelength (the 400nm range). Color Rendering Index is a measurement of how warm or cool a lamp is. Another simple explanation is: CRI is a measurement of how well a light source displays (or renders) colors to the human eye. The scale is from 1 to 100, and the higher the CRI of a given lamp, the better things will look to you. The wavelength of light is an absolute measurement of the actual colors (spectrum) produced by a given source of light. It does not change, though if we are speaking about aquarium lamps, a given wavelength of light produced by a certain lamp, may become reduced over time. However, the lamp will still continue to produce the exact same wavelengths on the spectrum scale that it produced when it was new. Those wavelengths will just not be as high over time, but they won't shift up or down the spectrum scale, and their ratios will still be the same. In the example shown below, for a 6700K power compact lamp, you see peaks in the 400nm, the 500nm and the 600nm spectra. Over time, as the lamp degrades, those peaks will lessen, but they will still be produced in the same wavelengths of 400, 500, and 600nm respectively. Wavelength is forever until the lamp burns out. It does not change. If you use a prism to defract (split up) a light source into the respective wavelengths it produces, you can actually see the a representation of the entire VISIBLE spectrum the light produces. Wavelength production is the most accurate way of describing a lamp, because it is not a relative measurement. It is an absolute measurement. That is why two different brands that have the same CCT (color temperature) of say, 10,000K, may look different. They produce light that has the same color temperature, but do so by producing different ratios of wavelengths on the spectrum scale. This is why though lamp manufacturers use CCT to describe a lamp's relative light color, they also usually provide a chart of wavelengths so you can see the ratios that created that CCT. I guarantee you that if you choose a lamp of suitable intensity, that produces the proper wavelengths necesary to drive a given biochemical reaction (like photosynthesis - and that's what this is all about!), and does so at the water depth where the reaction is to take place, you will have success. CCT (color temperature) is more complicated and is a relative measurement, in that it is related to wavelength, but is more a way to describe how the light will appear to our eyes. CCT is measured in degrees Kelvin, because color temperature of light refers to the temperature to which one would have to heat a "black body" to produce light of similar spectral wavelengths. A lamp with a low color temperature rating implies warmer (more yellow/red) light while a lamp with a high color temperature rating implies a colder (more blue) light. That is where the terms for "cool" and "warm" fluorescent lamps come from. In other words, to MIMIC light with wavelength properties that produced a color temperature of 10,000K, you would have to heat a totally black object (that could withstand the temperature), to 10,000 degrees Kelvin. See what I mean about complicated? Oh how I long for the days when we only used wavelength and intensity (in lumens) to describe light bulbs! CRI is the way a given source of light allows you to see the true colors in an object. That makes it a relative measurement, as we all see colors differently. However, scientists, in their effort to quantify EVERYTHING, have created a color rendering index scale, which starts at zero and goes to 100. Here's the scientific definition. I think you'll like mine better: "A method for describing the effect of a light source on the color appearance of objects, compared to a reference source of the same color temperature (CCT). The highest CRI attainable is 100." This means that a light source that has the same color temperature as the object it is illuminating will have a CRI of zero for that object, and the object will look black. As you increase the CRI of the light source, the colors of that object will begin to become apparent, and when the CRI hits more than 80, the color of the object will start to become vivid. As an example with fluorescent lamps, a typical cool white fluorescent lamps have a CRI of about 62. Lamps having rare-earth phosphors (specialty aquarium lamps are available with a CRI of 80 and above. The higher the CRI, the better.
  
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• The plants in my small (5 gal)aquarium are turning yellow. The aquarium has been running for about 3 weeks. The temperature is 78, pH is 6.8, and the tank contains 3 Angelfish. What have I done wrong?
  
  You didn't describe your lighting and that is where we think the problem lies. When plant leaves turn yellow, it is because the chloroplasts (cells that create food for the plant using sunlight) in the leaves are dying and that only happens if there's not enough light. You need to use two fluorescent strip lights, or you can buy a mini power compact fixture. You will replace the plastic hood that came with the tank with a glass canopy (see your local store) and set your improved lighting on top of that. You'll operate the lights for about ten hous a day. You also need to feed the plants weekly with a good aquarium plant food. By the way, a five gallon tank is too small for Angelfish.
  
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