I have an old 33g tank where the entire front panel of glass has developed a fog. I'm guessing it's a mineral deposit because I have liquid rock for water. I've tried scraping it with a razor and all different type of brushes to scrub it with but nothing works. I don't want to use any type of chemical cleaners but it's getting to the point where I need to drain the tank so I can clean it. Does anyone have any experience with how to get the fog off of the glass?

*Update*
I finally tried vinegar on the glass and it didn't work. I thought maybe if I uploaded a picture of it someone might be able to help me better or at least tell me if the glass is beyond repair. The darker spots are where the glass is clear which i think has to do with a very aggressive Chinese algae eater I had years ago. The weird thing is the glass wasn't foggy until long (maybe a year) after I had gotten rid of the fish.

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If it's simply deposits from hard water, put a towel on the floor and lay the tank down on it with the offensive panel resting on the towel. Pour a 50/50 mix of vinegar and water inside the tank so that it covers the inside of the panel but doesn't spill over the plastic trim. Just let it sit for a few hours. Take a razor blade to it and see if there's a simple white residue left behind that comes off easily. Don't be surprised if there's still a little haze left after it dries. It may take more than one shot if it's bad enough. Be careful with the razor blade near the silicone beads. Hopefully you didn't use anything abrasive in trying to clean it up and scratched the glass.

If it fails completely, the glass may very well be etched....permanently, which is essentially fatal.

vinegar and paper towel. Put a layer of paper towel on the glass and soak it with vinegar. Make sure it is all in contact with the glass and then leave it sit for at least 15 minutes, or longer.

Thanks I'll try the vinegar and hopefully that works. What would cause the glass to be etched? It got foggy before I ever tried to clean it with anything.

Could be simply hard water deposits or it may not even be that. It could be as simple as a light coating of film algae or bacteria that stayed on there long enough to turn rock hard.

If it won't come off with a razor that's not a good sign.

I'd try some CLR (it's very harsh so make sure you rinse it VERY well, let the tank dry completely, then go through another good rinse cycle before filling the tank).

If the CLR doesn't work, the glass is most likely permanently etched.

Now I'm worried I'm going to have to buy a whole new tank... Would it be safe to test the vinegar in a small area at the top with a paper towel if I lowered the water level with the fish still in it?

This should be safe to do, only add enough vinegar to wet the towel. Try to avoid getting anything in the water. Wipe the glass down after with a fresh paper towel.

I used a paint scraper - worked wonders and only took me a few minutes

Wait, So this tank has fish in it at the moment?

Yeah it does

Sounds to me like its a cheap acrylic tank. Hard water deposits do not form underwater.

Nope it's definitely glass. It might be biofilm that hardened like bushkill said. I was just guessing mineral buildup because my well water is extremely hard.

The paper towel trick still works. Just clip it to the rim of the tank or something so it doesn't fall in. Then only use enough vinegar to wet the towel.

I've done this in a stocked tank as well. Dry the glass before you do it just so you aren't diluting the vinegar.

So am I the only one having trouble understanding how mineral deposits can build up on a tank that's filled with water? At the waterline...sure. All over the viewing panels.......I'm stumped.