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Re: Cracked glass tops

>Date: Thu, 6 Sep 2001 22:03:30 -0500
>From: "Gary Lange" <gwlange at mindspring_com>
>Subject: Re:hotsie totsie
>Date: Thu, 6 Sep 2001 01:21:45 -0700
>From: "Robert H" <robertpaulh at earthlink_net>
>Subject: Re:hotsie totsie
>>>I just moved the All Glass  PCF on new tank I set up yesterday to discover
>the glass tank cover under the 2-55 w fixture to be cracked, which I believe
>was caused by the heat.<<
>I would be really shocked if that were true. Glass can take a lot of heat
>before cracking, unless the glass is defected. I dont see how a PC could
>ever get that hot. I know people who run combinations of high wattage metal
>halides and PCs in a closed hood inches away from glass. It dont compute!
>Robert Paul H
>The 1/4 inch glass under my 2, 2 x 55 watt (3 foot fixtures) cracked too.  I
>did use glass that had been sitting around in someone's garage for several
>years and chalked it up to funky glass.  The All Glass lights ARE much
>hotter than the AH lighting systems though.  I didn't take them apart to see
>if they have the same sort of ballast but I know their reflector doesn't
>hold a candle to the AH stuff.  I have 4 x 55 inside (4 foot hood, by AH )
>sitting right next to the All glass lights.  They are warm but they just
>don't produce the same amount of heat.  I'm much more careful with the glass
>now and make sure that the 2 lights are several inches apart to avoid a
>repeat.  On the AH "box" I put a 1/4 inch "bumpers" on the back 2 corners so
>it tilts up slightly in the back.  I think if you could raise these just a
>bit off of your glass it would help with the cooling.  Hope you used the
>vents that come with the retro-fit kit too when you plop them into those
>plastic hoods.  They don't have enough venting in them.
>Gary Lange
>gwlange at mindspring_com

My local glass shop reccomends 3/16" tempered glass for all aquraium tops. They tell me that this can handle 425 degrees F with no problem at all. This I learned AFTER picking up 1/4" regular glass for my ancient, stainless steel cornered, slate bottomed 55 gallon tank. We'll it's been over a year with  2 X 55 PCF's ( from AH Supply)  retrofitted into an old perfecto Double Bright strip light and an Oceanic 2 X 55 watt PCF strip light, both resting directly on the glass and no problem whatsoever with cracking. If I were to do it again ( or is it when !) I will be using the 3/16" tempered stuff. The difference in price would have been $17.00 for 1/4" window glass VS and $27.00 for the same size....certainly not a really large difference.
Bob Buettner
Still in the NW CT hills