Lighting: Duration vs. Intensity

> From: "John Y. Ching" <jyching at watnow_uwaterloo.ca>
> According to the formula in the Plants FAQ for calculating the optimal
> lighting intensity and duration for different plants/tank setups, I need
> to leave my lights on for 13-14 hours. 

If the plant FAQ has duration as part of the formula, I would discount
it's usefulness.  You can't make up for low intensity by leaving the
lights on longer.  

> In a recent post, George Booth said that he only kept his discus tank
> on 9 hours a day due to algae problem.

Karla mentioned that it's really 10 hours/day if you count the hour
the lights are on in the morning for feeding.  Also, there was not an 
algae "problem", just a little more than we like. 

> My question is: does algae like more intensity or longer duration? 

Difficult to answer.  My opinion is that algae is opportunistic; it
will use what it can.  If the lights are on too long, the algae can 
begin to use nutrients after the plants "go to sleep".   

> I think I can add two more single flourescent fixtures to my custom
> hood, but I am concerned that the algae problem would get worse. Do
> you think adding two more lights (+80watt) and reduce the duration
> (9-10h/d instead of 13-14) would reduce to increase algae growth? What
> about plants?

The exact amount of light is really dependent on a lot of things -
types of plants, available nutrients, depth of tank, etc.  Do you have
an algae problem now?  It's very "trial and error" to see what works
for your situation.

> If I do add two more lights, can I just use cool white bulbs for the new 
> lights? Not sure if I can keep up with these $25.00 Tritons...

Sure, they will add more light.