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