Hi,

I know the general rule of thumb is 2-3 Watt per U.S. gallon, but of course
it's only a rule of thumb and seems rather imprecise to me, since watts
measure power while gallons measure volume, so measuring light intensity
with power/volume seems illogical in the least. The rule also has a long
list of assumptions, which are not always true (as in my case), so I'm
quite at a loss about how to find out if my plants are getting enough light.

I currently have a 20 gallon (24" x 12" x 18") aquarium which is moderately
planted, but the plants don't really grow (they actually appear to be
slowly dying) and I'm trying to find out why. CO2 level is adequate for
the aquarium (around 15 mg/l during the day), so that doesn't appear to be
the limiting factor. The substrate contains 50% Flourite and the aquarium
has been going for half a year, so it should contain all the required
nutrients. The next thing to consider for me were the lights, but here, as
I said before, I have no idea how to proceed.

The lamp that I'm using is a bare-bones fluorescent fixture with two 32W,
T8 strips. There is no reflector and the lamp is hanging about one feet
above the uncovered aquarium. The total power usage is 64W, which using
the rule of thumb mentioned above should be more than enough, however,
since the lamp is not positioned directly on top of the aquarium, I feel
that the rule of thumb doesn't work that well. It is also twice as long as
the aquarium, so the light intensity is even lower, but I might be wrong.

The question is, are there any symptoms that would tell me that my plants
aren't getting enough light? And if they aren't, is there anything I can
do to increase the light intensity short of getting a compact-fluorescent
fixture to put directly on the aquarium?

Thanks in advance!

Richard

--
"I know not with what weapons World War III will be fought, but World War
IV will be fought with sticks and stones." -- Albert Einstein

Richard Krush wrote:
I currently have a 20 gallon (24" x 12" x 18") aquarium which is moderately
planted, but the plants don't really grow (they actually appear to be
slowly dying) and I'm trying to find out why. CO2 level is adequate for
snip
The lamp that I'm using is a bare-bones fluorescent fixture with two 32W,
T8 strips. There is no reflector and the lamp is hanging about one feet
above the uncovered aquarium. The total power usage is 64W, which using

Well, since you don't have a reflector, at least half the light from
the bulbs is being wasted (not being directed at the tank). Also since
your bulbs are longer than the tank, only the fraction of the bulbs that
is actually above the surface of the water should be counted.

aren't getting enough light? And if they aren't, is there anything I can
do to increase the light intensity short of getting a compact-fluorescent
fixture to put directly on the aquarium?

I would get a compact fluorescent or at least a reflector installed.

--
Victor M. Martinez

http://www.che.utexas.edu/~martiv

Richard,

I'm pretty sure that you are not giving your plants enough light, considering
that your bulbs are twice as long as your aquarium and hung a foot above the
water surface. The W/gal rule is not absolute (see my discussion of it in my
Notes page at my web site), but for your 20g tank size, you should aim for
closer to 3 W/gal, with the entire amount of light shining into your aquarium
and not wasted outside of the aquarium, and the lights six inches or less
from the water surface. That means you should get three 20W fluorescent
bulbs, or go to Power Compacts.

Good luck,

Hoa
Aquarium: http://www.geocities.com/nguyenhg/

In article , Richard Krush
writes:

Hi,

I know the general rule of thumb is 2-3 Watt per U.S. gallon, but of course
it's only a rule of thumb and seems rather imprecise to me, since watts
measure power while gallons measure volume, so measuring light intensity
with power/volume seems illogical in the least. The rule also has a long
list of assumptions, which are not always true (as in my case), so I'm
quite at a loss about how to find out if my plants are getting enough light.

I currently have a 20 gallon (24" x 12" x 18") aquarium which is moderately
planted, but the plants don't really grow (they actually appear to be
slowly dying) and I'm trying to find out why. CO2 level is adequate for
the aquarium (around 15 mg/l during the day), so that doesn't appear to be
the limiting factor. The substrate contains 50% Flourite and the aquarium
has been going for half a year, so it should contain all the required
nutrients. The next thing to consider for me were the lights, but here, as
I said before, I have no idea how to proceed.

The lamp that I'm using is a bare-bones fluorescent fixture with two 32W,
T8 strips. There is no reflector and the lamp is hanging about one feet
above the uncovered aquarium. The total power usage is 64W, which using
the rule of thumb mentioned above should be more than enough, however,
since the lamp is not positioned directly on top of the aquarium, I feel
that the rule of thumb doesn't work that well. It is also twice as long as
the aquarium, so the light intensity is even lower, but I might be wrong.

The question is, are there any symptoms that would tell me that my plants
aren't getting enough light? And if they aren't, is there anything I can
do to increase the light intensity short of getting a compact-fluorescent
fixture to put directly on the aquarium?

Thanks in advance!

Richard

--
"I know not with what weapons World War III will be fought, but World War
IV will be fought with sticks and stones." -- Albert Einstein


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I would agree with Noa and would like to add: a "rule of thumb" is a
"rule of thumb", doesn't mean it's logic but statistically viable.
It's based on best results acheived by most. The idea is to give an
easy relation between light and a common parameter, the volume. No
need for complex calculations and it gives good results!

If you wan't to find out more and understand i suggest you go on
thekrib, there is some info. It's related to a lot of factors but can
be calculated precisely.

Andre