On Mon, 15 Dec 2003 22:05:09 GMT, "Michi Henning"
wrote:

"John Little" wrote in message
...
I have a 400 watt metal halide on a 90 gallon corner style aquarium. I have
the choice of a 20K or 10K bulb. Wondering which one is the best for a
planted tank with Discus.

I have a smaller tank with 10K pc bulbs and that tank is doing fine. I was
just wondering if a 400 watt metal halide is too much for a plant tank.

That's a bit over one watt per liter. You can do that, but will have to use
CO2 injection (and do a lot of weeding, I suspect). Plants will grow
very fast at those light levels.

I'm concerned about the color temperature though. Most people use
5000K to 5700K for planted tanks. Higher color temperatures
encourage algae. (I've never tried using 10K on a planted tank
myself -- I'm just relaying advice I've received from a few experienced
people.)

Cheers,

Michi.

I would have to agree with Michi, don't waste your money on 10k
bulbs-they are designed for reef tanks. Corals that have symbiotic
algae are in deeper water and only the blue end of the light spectrum
can penetrate to those deeper levels hence the actinic and 10k bulbs
are marketed for reef tanks. You can even go as low as 4000 4500k
for a planted tank if you don't want of spend $60 for bulb.