This article is from the Aquaria: Plants FAQ, by multiple authors.
If you can fit a second tube in your existing hood, many stores sell
upgrade kits to add the second fixture. Otherwise, you might be able
to add a second hood to the tank, or you can find a replacement
two-bulb hood (mail-order places sell them). Another option for 4-foot
(130cm) long tanks is to buy a "shoplight" fixture and lay it across
the top over the glass. You can also build your own hood or canopy and
mount the shoplight or fixture inside. It's possible to omit the
fixture by purchasing special end caps and clips for the tubes. These
are available, with ballasts, from aquarium stores and are commonly
used by marine aquarists.
 
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