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[APD] Re: Red Plants suntans and K ratings

Phil Edwards said: "My hypothesis is this: Since a plant produces red
pigments to capture blue
light, then a plant grown under a higher K rating bulb (more blue light)
should be more red than if it were grown under a lower K bulb."

I am sure that you will find this to be true.

The red pigment I believe also absorbs the blueer wavelenghts: violet and
ultraviolet. That explains why many land plants here in sunny Malta turn red
/reddish/brownish at the approach of summer, to protect themselves from
harmful UV  rays, much like tourists turn from white to brown. Their melanin
absorbs the harmful UV rays. (Some of the tourists do turn reddish (g), but
that's because their melanin production wasn't activated quickly enough)

As I understand it, most aquarium red plants  are also sun-loving plants,
requiring high light intensities. They are red because they need the UV
protection. More UV/blue light in the tank will therefore intensify their

But then why are deepwater algae red/brown? They don't need the UV
In their case it is because the bluer wavelenghts are all that is left as
you go deeper. Since a red pigment is more efficient at trapping these
wavelenghts than chlorophyll, it is the reddish plants that would
predominate at depths.

There are low light aquarium plants that are red/brownish too. My Crypts are
green in the light but the same plants turn brownish when the light
intensity is reduced. I think they do this to absorb the bluer wavelenghts
that are associated with darker deeper water(?). My lotus is also a dark
deep red in the shade, stays low too.

But brown algae (diatoms) due to their pigment, also utilise the blue
spectrum. Maybe that is why they predominate in darker aquariums. And I am
sure they prefer the higher K rates (bluer/UV spectrum). I find that their
presence always increases when I shift to 10000K or grolux (pink) tubes.

(Tom Barr please correct me if I am wrong.)



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