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Re: clouded glass

Michael D. Nielsin wrote Jan. 13:
>It is highly unlikely that you are actually having the glass dissolve
>before your eyes.  I read at one point that while glass does dissolve in
>water, it is a slow and minute process taking many years before changes
>can be measured.
>From the process you describe it is far more likely than some other
>material is being deposited on your glass as you refer to the wetting and
>drying of the glass top.  If is was the glass dissolving it would occur
>faster with constant submersion.  The experiment I have heard about
>involved grinding glass to a powder and placing in a sealed container for
>several years with only a small portion being dissovled at the end of this

I am still convinced that the process is the dissolving and redepositing of
the glass.  Every night water condenses on the glass cover and every day
the heat from the lights dries it out.  The water that condenses is free of
SiO2, which can not be carried along in the water vapor. Therefore,
conditions are ideal for the dissolving of the glass. In contrast, dipping
glass in water would not dissolve as much because most water is already
either saturated or close to saturation with SiO2.  Besides, it is not the
dissolving that causes the problem, it is the redepositing.  The same
process of clouding can occur in a double window if water gets inside.  I
just moved into a house where we asked the previous owners to replace a
window that was severely clouded by moisture.  When water is inside the
window the daily cycle of temperature changes causes a cycle of
condensation and drying that is similar to what happens on my tank tops.
The deposit is certainly not calcium and it is as hard as glass and as
resistant to chemicals.  Perhaps if glass were immersed in water free of
SiO2, it would dissolve faster because it would be in this water 24 hours a
day.  The part of the process that makes it a problem for me, though,  is
the redepositing in cloudy rings that define the edges of the condensation
drops.  A few years of this process make the glass so cloudy that it cuts
out a significant amount of light.

>However if it is glass simply get some Hydrofloric acid and this will
>dissolve the glass deposits and the glass quite nicely.  Look at a hobby
>store where glass etching is done.

The problem is that I want the glass clear with a smooth surface. Glass
etched with hydrofluoric acid would also interfere with light transmission.
I probably need to find out just how much it does interfere.  One of these
days I will try to make measurments with a light meter and new, versus old,
clouded glass.

>Date: Tue, 13 Jan 1998 09:22:02 +0100
>From: "Simone e Pierluigi Vicini" <psvicini at mdnet_it>
>Subject: Solid fertilizer and 100 mg/l of NO3
>Hi everybody,
>                    after one week of using that solid fertilizer my NO3
>went at 100 mg/l and I had to do a water change for my fishes, but no algae
>activity till now.
>What I don't understand is this: I added 15g of that solid fertilizer
>(14-5-14) that means 2.1g of total nitrogenum that means 42 mg/l of N in 50
>litres if it is already totally dissolved.
>Supposing that all the nitrogenum was converted in NO3 it will mean that I
>could have not more than 170 mg/l of NO3 if those 42 mg/l of N were totally
>converted. Is this right?
>Next I will use less fertlizer and maybe I will add smaller amounts more
>often. The results are incredible.
>Hope you can help
>Simone Vicini (psvicini at mdnet_it)
>End of Aquatic Plants Digest V3 #22
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Paul Krombholz, in soggy, cloudy Madison, Mississippi