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Re: Mercury Vapour or Metal Halide ??

>  Metal halides are the wrong spectrum. They contain to much blue light and
>  so encourage algae, this means they are ideal for the marine
>  aquarium. This is because blue light penetrates salt water very well ( red
>  does not ) and so sea plants have adapted to this. The reverse is true for
>  fresh water plants, they are similar to land plants and use light more to
>  the red of the spectrum i.e. mercury vapour light.

	This is true if you were going with a MH bulb like the 20000K or
10000K bulbs, but they do have 4200K bulbs and lower which will function
well for freshwater plants.  Hydroponics shops use these bulbs as well and
if you check major internet sites discussing hydroponics you'll see them
discussing their use for water & land plants.