Glass or Plexyglass top?

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AC2020x

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Dec 31, 2008
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Hey, I need a top for my tank because i'm looking into getting some fish which will jump. Would Glass or Plexy glass be a better choice? Which would let more light though cause I do have corals in the tank though none that need very high lighting right now. Also what about the air circulation. Obviously alot less air will enter though there will still be open spaces thoughout the top-- is this ok??? Thanks alot!!!
 

Ace25

www.centralcoastreefclub. com
Oct 3, 2005
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Glass without a question. I tried plexi at first.. it melts/bends/distorts very easily when under lights.. even my PC lights warped the plexi. I even tried Lexan thinking it is much stronger than normal plexi and that didn't work for me either.
 

Ace25

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Oct 3, 2005
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Yup, I have a glass top on my 29G and there is very little difference in light penetration, and I spent some time staring at the tank and taking the top off and on to see if I could tell a difference.. not really. I do have to clean it once a week because algae starts to grow in it, but a quick swipe with paper towels does the trick.
 

redfishblewfish

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Nov 19, 2008
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The correct answer is neither.

Glass actually cuts out a considerable amount (I think something like 60%), of UV wavelengths that are needed for coral growth. If you must cover, and you don’t want to use some other means (egg crate, aka light diffuser), your only choice is polycarbonate. This is not plexiglass, which is actually a cast acrylic.
 

GregAW

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Aug 25, 2008
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I tried plexi at first.. it melts/bends/distorts very easily when under lights.. even my PC lights warped the plexi.
The Plexie glass will distort just from its own weight. I've got a piece on my frag tank and it'll droop through the night without lights. Not to mention, it seems to collect salt very quickly and steams up. The combination of salt and condensation will cut out a lot of light.
 

The Zigman

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Oct 5, 2007
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All plexi is NOT created equal.
If you are using polycarbonate, and it is distorting under its own weight, then you need something thicker.

Clear Acrylic is near garbage.
Lexan is Polycarbonate... But there are different grades of lexan that are intended for different uses.

Lexan® 9034 sheet will transmit 86% of the light.
Lexan® Sheet (Lexan 9034) is UV stabilized, has a heat deflection temperature of 270 degrees F at 264 PSI, and has a smoke density rating less than 75.
Lexan® 9034 is engineered for window glazing as well as for sign applications. In addition to colorless (clear),
Lexan® 9034 is available in solar gray and bronze in thicknesses from .080" to .500". Lexan® 9034 uncoated polycarbonate sheet is the standard grade of Lexan® sheet for general purpose applications.
High-impact Lexan® 9034 can be used for economical protection against breakage or intrusion."
 

kcress

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Apr 9, 2005
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Acrylic sucks up water like a sponge. This causes it to swell up. If you put a tight piece of plexy into a glass sump as a divider it can break the sump as it swells over the next few days.

The side facing the tank will absorb more moisture than the side way from the tank. What happens is the wet side expands. Being longer on one side causes the nasty bowing. The "belly side" is the expanded side.

You can try all sorts of things to try to reduce this. The only really effective one is to just make the piece so stiff it can't bend. That means gluing some tall pieces on one of the sides, think, 'euro bracing'.

But as redfishblewfish mentioned any clear material seriously reduces light transmission.

Better would be to use very fine netting with holes only as small as absolutely necessary.

You can also use surrounds too tall for the jumping fools. Make black plexy rectangles that perfectly fit on your tanks rim lip. And just set them in grove. These are nice because they block the light from dazzling a person viewing and usually don't restrict your working in the tank at all.
 

GregAW

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Aug 25, 2008
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Or you can go to your glass shop and get some Star Fire glass cut to fit the top.
 

thincat

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Jun 10, 2008
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Glass and Acrylic tops are bad Ideas. the worse thing is it traps Co2 gas and causes your PH to drop. Better to use 1/4" netting with either an alum. or plastic frame. Lets gases flow freely and stops fish from jumping out. IMO
 
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