Hi Fish Nutter,
Sorry, I got distracted and did not put together your other post with the one here. I gave the wrong advice here. If you are still running those marine lights I feel it would be a good plan to work on replacing them with lights of a K rating more appropriate to a freshwater setup. I disagree with your shop person about you needing such high K ratings for plants in a freshwater setup and I agree with OM47 that those 15K/18K Kelvin rated lights will promote algae with all the extra blue spectrum they have.
[Note: The subject of light and all the measures we use surrounding it to help ourselves try to understand the color, brightness and energy involved in what we are seeing is truely complicated and confusing. Talking about the "Kelvin temperature" of light has to do with a scale based on the spectrum of light radiating from a "black body" where lower K numbers represent a more reddish color and higher number represent a more bluish color.]
[Note: Another lighting thing to understand is that the "T" numbers associated with fluorescent lights are simply a fluorescent lighting industry shorthand meaning "T for tube" and [number] for number of eights of an inch of diameter of that tube. So "T8" means its a tube light where the diameter is 8 eights of an inch in diameter, ie. 8/8 inch or 1 inch in diameter. As often happens, using an industry shorthand is a way to make something simple seem more complicated!]
Its not that algae can't take advantage of all the different colors (or spectra if you will) of light out there, they will! It just that blue light can make iron more available in the aquarium (the blue light drives a reduction reaction were iron ions bound up in big organic molecules we call DOC (for dissolved organic carbon complexes) get oxidized, freeing up the iron.) It is believed that iron may be a limiting nutrient for many of the common forms of algae we deal with in the aquarium.
Anyway, in this post I just wanted to say that at some point you should indeed be looking ahead to having your tubes be a color that matches a more normal green-yellow-white light (for instance 6700K) that freshwater plants in streams would be seeing, not the super blue-white that the coral-bound algaes in the caribbean see from the noon sun!
All this "color" stuff is a different thing from the "basics" of being in the right efficiency range (wattage of a particular type of tube light) and exposing the leaves with a number of hours that has them growing well but leaves less excess for algae. Sorry this all sounds so complicated.. its probably just that I'm not organized or smart enough to write it up in a simpler way!
~~waterdrop~~
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