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Re: tank covers

Ivo wrote:
> In the thickness range used for aquarium covers, both materials are
> indistinguishable from each other for all practical (plant) purposes.
> I would say that you should use the plexiglass, since it doesn't stain
> as much as the glass. Doesn't it bow under its own weight ?

"Plexiglas" or any acrylic is very hygroscopic. It swells a lot on the wet
side, so the bowing is from that, more than from weight. Not a good idea,

Soda-lime glass does absorb some of the precious red part of the spectrum,
but at 1/4" it is probably only about 10% of the useful light out there.

Polycarbonate ("Lexan") seems better behaved as a cover and has excellent
transmission across the useful plant spectrum. I sometimes use the
polycarbonate plastic panels used to cover fluorescent fixtures for the
purpose. They are too thin and flimsy for anything but small tanks, tho.
Thick "Lexan," as used for unbreakable window glazing is expen$ive!


Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

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