06-09-2011, 08:13 PM
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Originally Posted by Byron
Agree, it is likely that you bought tubes that do not "fit" the existing fixture.
The common fluorescent tube fixtures are what we call T8. The "T" number refers to the diameter of the tube that will work in the fixture, and the number is in eighths of an inch. So a T8 tube is 8/8 in diameter, or one inch obviously. The older type of fluorescents were T12, the tubes were thicker, 12/8 or 1.5 inches diameter. These are still available and will "fit" the same fixtures sort of, although they are being phased out by manufacturers because the T8's use less energy and are more efficient. Also, the newer T8's may "light" in the older fitures but sometimes with other issues, and this can be dangerous.
Then there are T5. These are 5/8 of an inch diameter, and will not work in T8 fixtures. And T8 tubes will not work in T5 fixtures.
There are others too, though I have not myself tried them.
Check the tubes that came with the fixture, and if they are T8 then that is what you must get to replace them. If T5, same.
Now to the appearance of the light. This depends entirely on the phosphors inside the tube that "burn" when the light is on. Manufacturers can vary the colour of light emitted by different phosphors. The colour temperature as it is called is measured in degrees kelvin, and will appear such as 6500K, 5000K, 10,000K etc. Mid-day sun is around 5500K. Lower kelvin numbers indicate a "warmer" light, with more red/.orange in the mix. Higher numbers like 10,000K indicate a "cooler" light with more blue/purple in the mix. How you light the tank is up to you, unless you have live plants.
If you have plants, you should get a "daylight" or "full spectrum" type of tube. These will have a kelvin rating between 6000K and 7000K. They provide the best plant light, and colour rendition of your fish and plants will be very close to the mid-day sun.
Thanks for all of your info! I checked the bulbs...the old bulbs say GLO Sun-Glo 24'/61cm 20W T8, the new say F18W - T8 - AR - F&SA on it. it appears they are the same size... any suggestions what else the problem could be? Thanks!