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So I got my 90 gallon off of Craigslist, and finally got it filled up with water. I now notice some scratches on the glass, as well as some serious spots on the outside. Unsure what the spots are, but they disappear when I initially clean the glass, then immediately reappear. Is there anything I could purchase that could take away the fine scratches on the glass, and any cleaning substance to get whatever the spots are on the glass, off? I need help, I want to make this aquarium look like new again, if it's possible. Not sure how old it is, but it does look nice, and noone would probably notice the spots unless they got up real close. But I know they're there, and it bothers me. I'll try to get a photo up here to show. Thanks!

You can polish glass scratches with jeweler's rouge paste, a buffer or power drill with buffing pad, and a lot of patience. Yes, you WILL have to drain the tank if the scratches are on the inside, and probably turn it on it's side (carefully) for easy access, because it will take a while. I reccomend you start with a medium grit and then go to extra fine. This trick works with car windshields, too.

The spots on the outside are probably hard water stains. You can polish them off with the same extra fine jeweler's rouge, or use liquid CLR. But DON'T use CLR on the inside, where the residue will contaminate the tank water.

Thank you very much, will get some tomorrow and give it a try!

Ok, so CLR did not work. I'm thinking it's from being a saltwater tank, in fact I'm pretty sure it is. So this could be real hard salt water residue or something. It almost looks like it's on the inside, but it you wipe it on the outside, it does disappear, and then quickly re-appear, so that's why I'm pretty sure it's on the outside. It looks horrible, and there's got to be a way to clean this, or remove all the marks. Any other suggestions anyone? I appreciate the help.

CLR is extremely acidic IIRC, so if that's not doing it for you, try something at the other end of the spectrum like bleach. Maybe see if you can't scrape it off with a straight razor.

I'll try the razor, although you can't really feel it on the glass. Tried bleach AND gas, lol, still didn't work, GRRRRR!

I have removed stains off of glass on cars with Mothers wheel polish. You can get it at any auto parts store or a Walmart. That stuff cleans any surface!!

How bizarre. Have you tried soaking a rag with the CLR and leaving it up against it for a bit? Maybe acetone? How many sides is it on?

Yes, it's VERY bizarre. It's mainly on the one, long side, pretty much the entire length, and a few minor spots on the other. The ends are clear, thankfully, but the one long side is horrible, and very noticeable. I thought of acetone, but I don't know, we'll see. It's definitely a challenge to figure out what the heck it is and how it's gonna come off. It was previously a salt water tank, so it's gotta be a hard, salt residue or something deep into the glass. I'll let you know, thanks for the suggestions.