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Re: Deposits on Glass

> Date: Sun, 20 Sep 1998 23:12:25 -0500
> From: Andy Dilbert <ixtapa at geocities_com>
> Subject: Deposits on Glass
> Hi all,
> To all who don't recognize me, this is Andy Dilbert, off and on member of
> the APD.  I'm 16, and setting up my 55 gal to become a plant tank.  Right
> now it's sitting outside in the rain, because I can't seem to get it clean!
>  It has deposits on the glass...I think they are SiO2 deposits.  I used to
> have some fish in there, but I neglected it until the the substrate had
> patches of black, and the calcium deposits on the glass were translucent.
> I moved all the fish (about 5 tetras....it wasn't heavily stocked!) into a
> temporary tank, because the 55gal tank needed serious cleaning.  I removed
> the calcium deposits with Muriatic (weak HCl) acid, and scraping.  But
> there still are rings on the tank, in two places:  the water line, and
> where the water met the sand substrate.  How can I clean these deposits off?

Hi Andy,

I hope someone else has a better answer than mine. I have a 55G with
nearly the same problems, but the faint "frosting" covers nearly the
upper third of the tank. It becomes less obvious when full, but the
surface clearly favors attachment of algae, etc. in that area. There are
rings where it is more obvious.

I have concluded that the problem is not deposits, but actual etching of
the glass by alkaline water. Much soda-lime glass is actually slightly
soluble in alkaline solutions, and this tank was probably used a long
time as a reef or salt-water tank, before I got it as a "bargain."
Either the pH of typically 9+ or the action of inverts has eaten into
the glass itself. It looks like a deposit, but I'm pretty sure it is

Since the glass and the water have similar index of refraction, the
surface tends to *almost* disappear when the tank is filled. Most
deposits would not have an index near enough to 1.5 to vanish like that.
I do wish it was easier to clean in those areas, tho.


Wright Huntley, Fremont CA, USA, 510 494-8679  huntley1 at home dot com
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