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OK guys i have a question. Y shouldnt we use blue light fluorescent in a tank? I use to have 1 15 watt white color and 1 15 watt blue color. So i changed the blue one and got another white light 15 watt. So now i have 30 Watt light when i turn the together. My tank is 10 gal tank. Just tell me y the blue light isnt good for a frshwater tank. When i use to have 1 15 watt white light turned algea use to grow up. And now when i have the 3o watt no more algea grows. Was the problem from the blue light. And how long should i keep the 30 watt light on. I have 3 goldfish. ( I know over stocked).

10x

Hi,
It is not that you should not use actinic blue light
in a tank, rather it is that you do not need to in most
cases.

Part of the use of the blue light has to do with the
depth of a tank and part has to do with what creatures
are living in the tank.
Depth - As light travels through the water it is scattered
by the debris in the water and the result is that some
parts of the spectrum penetrate deeper without being
scattered. Light at the lower, red end of the spectrum
is scattered within the first few feet, while light at
the higher end of the spectrum penetrates many feet before
it is scattered. Fish keepers take advantage of this
when they have deep tanks. Generally speaking tanks of 24
inches deep or more will have lights that are 10,000K or
higher in the hood. Some of these higher rated bulbs are
called "actinic blue."

Creatures - Reefs are nearly all clustered along the
equator, and are very shallow. Some of the invertebrates
that live in those reefs use the tropical sun to form
symbiont algae that they live off and or provide some of
the very vivid colors that they have. In aquariums this
harsh bright light is duplicated by the use of light bulbs
in the 10,000K to 20,000K range and are usually either
metal Halide (MH), or Compact Fluorescent (CF) lights.
Again, the blue end penetrates the depths of their tanks
with nearly all the energy intact.

The problem with the lights at the blue end of the spectrum
is their effects on what the human eye sees. In some cases
the bluish light, if used alone, will wash out some of the
shades of green making them appear dull. Usually, folks
with either saltwater or freshwater tanks that use the
blue bulbs will mix them with a "white" bulb, something
around the 6700K to 8800K range. The blend of the white
and the blue helps cancel the "washout" effect and you see
more realistically what is actually there in the tank.

Using a "blue" bulb in a 10G tank is completely
unnecessary because of its shallow depth - Unless - you
are keeping the tank as a mini-reef with invertebrates
in it.

As for the Algae, that is a matter of how much light you
had in the tank vs the availability or lack of
availability of nutrients. Algae is an opportunistic
critter. It takes advantage of a situation that is out
of balance. Too much of one element and not enough of
another, or others, will give algae an opportunity to
thrive. If things such as, fish, fish waste,
water changes, gravel vacuuming etc are done regularly,
and there are enough plants in the tank to take up
the nutrients along with not too much light, and conversely
not too little light, then chances are you will have very
little, if any, algae.

Hope this helps...
Frank

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

I actually like how a half blue tank looks. Plants though do not seem to use the blue light as well without an equal amount of red light. Tons of blue light will still grow plants but not as well as if you have an equal amount of other spectrums with it. That means most of your blue light is wasted and goes to growing algae instead. Algae is quite efficient at using blue light and grows well in it. Kinda like you can grow plants in incandecent light but it has such a limited spectrum that much of it goes to waste. With a full spectrum fluorescent you can grow plants better with less light because they have a more equal spectrum and can use all the light. You can use all the blue light you want but you have to take into account that it won't grow plants as well and will grow algae very well. My tank is half blue. But I have a huge excess of light on the tank(6?wpg) and tons of low to mid light plants so I don't need the extra watts and the algae still doesn't have a chance to grow.