cleaning second hand tank

On Sat, 15 May 2004 00:45:41 +1000, "Desmond Wong"
bubbled forth the following:

Hi,

Any ideas on the best way to clean a second hand tank? I have aquired one,
and found that because the previous owner kept it only half full, the bottom
half of the tank is quite clean, but the top half has this white film-like
substance on it.

I have tried using water and a razor blade, doesn't seem to lift. What would
be safe to use on it to rid this stuff?

Des.

I had a similar problem with an old MetaFrame 30 Long (44L x 14H x
13W) a friend gave me. Only 1/3 full of water for most of a year, the
top 2/3 of the tank was very crusty. Most of it scraped off with a
razor blade, but the last bit of film/cloudiness wouldn't go away.
Vinegar, CLR, hydrochloric acid, sulfamic acid, nothing would remove
the film/cloudiness. There were also a few deep scratches where
gravel had been scraped up the side of the glass, and numerous faint
scratches, the kind that are visible, but can't be felt

I finally realized that the mineral deposits had actually etched the
glass. I went to the local rock shop, bought a small bag of cerium
oxide(have 90% left), an 8" leather polishing pad (I would recommend
felt rather than leather), and a tube of feathering disk adhesive to
stick the (trimmed) pad to a 5" backing plate for my electric drill.
About $15 total, $8 of that was for the tube of adhesive (big enough
to do a couple hundred tanks at least, but I can use for woodworking
projects, so it will get used).

Mix up a paste of the cerium oxide with water about the viscosity of
hot maple syrup, and polish away, keeping the surface wet with a spray
bottle. The cut off pieces of the pad can be wrapped around a stick or
used with a dremel tool to get in the corners.

It took about 45 minutes to remove the cloudiness from the 4 side
panels, as well as polishing out the small scratches, and another 20
minutes doing the outside glass and the stainless steel frame.

The deeper scratches didn't come out, but the edges were smoothed out
so they don't catch the light as much making them less visible. I
would need to start with a much coarser grinding compound to remove
them -- they weren't bad enough to spend the time grinding out, plus
it would weaken the glass more than just leaving them as is.

Rinse the tank very thoroughly, then wipe it down with damp paper
towels to remove the cerium oxide. I don't think it would be poisonous
to the fish, but it is a very fine powder that if left in the water
could irritate the fish's gills.

The end result? When the guy who gave me the tank saw it after I had
set it up, his first question was "How much did it cost to replace the
glass?" It actually came out better than I thought it would.

HTH

Jerry