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Re: Cleaning Glass

>Bob Dixon wrote:
>Subject: Re: Cleaning Glass
>Paul writes:
>> The deposits on my tank tops result from a process where water condenses on
>>  the tops during the night when the lights are off and then dries up during
>>  the day when the lights come on and heat the tops.  Glass is dissolved
>>  during the night and then redeposited during the day.
>Are you serious?  What makes you think this is aluminum silicate?  how can
>you tell the difference between glass and carbonates?  What is in your water
>that will eat glass?   The only thing I know of is hydroflouric acid, and
>that's not likely to be floating around in the local water supply.

I never said it was aluminum silicate.  I said it was redeposited glass.
The deposit is, I am pretty sure, silicon dioxide.  It is easy to tell the
difference between glass and carbonates.  The latter are much softer and
are dissolved by acid.  The former is much harder and is not dissolved by
acid. I have tried full strength, 18 molar hydrochloric acid on it, with no
effect.  Muriatic acid is only 20% hydrochloric acid.  Silicon dioxide is
the major component of glass, and it is somewhat soluble in water.  The
water that condenses on the bottom of the glass plate dissolves a little
bit each night, which gets redeposited during the day.  If you don't
believe that silicon dioxide is slightly soluble in water, how do you
explain where diatoms get their silica shells?

>From: Zxcvbob <zxcvbob at tcw_net>
>Subject: Re: cleaning glass
>> This deposit is glass that has been dissolved and redeposited.  Muriatic
>> acid (hydrochloric acid) won't touch glass.  It is good for getting off
>> calcium carbonate deposits.
>I'm suprised that this can build enough to cause problems in just 6
>months.  But assuming you are right, you might want to use acrylic or
>polycarbonate plastic ("plexiglas") instead of glass next time you
>replace the panels.  Plastics should be immune to the disolve/redeposit
>problem.  You should be able to get the plastic panels from your local
>glass suppliers.
The problem with plexiglass is that it warps.

Paul Krombholz, in Central Mississippi, where we got at least an inch of
rain Saturday.