Removing STUBBORN silicone

[AE1752]

Hey guys!
I found a deal on a 180 for my puffer who needs a knew home after a previous blowout. The silicone was okay and the tank was holding water when I picked it up. After cleaning, I realized the algae in the corners was actually underneath the silicone in the corners and peeling up. I decided to reseal and got all of the silicone out. However, there are still circles and hard water stains. I have used everything on these circles! Razors, acetone, bleach, vinegar, cabinet grade steel wool, 98% alcohol with no avail! Oddly, the circles are spots where there was algae that has since been removed with the majority of the silicone. But if touched you can absolutely feel them. How do I get it off?! Is there a secret?? I'm close to trying power sanders or throwing in the towel... I don't know if it is relevant but this was a freshwater tank previously, which is why the algae stains really bothered me. Tank has a manufactured date of 1994 on it, is it too old to be revived?

 

[blaxsun]

With the exception of EzeClean (rather expensive), you've probably tried everything else short of sandblasting - so I'm honestly not sure what to suggest. You could try making your own citric acid mix and letting it soak. My OCD feels your OCD pain...

 

[ISpeakForTheSeas]

The only thing I can think to add is (assuming you used household a.k.a. white/distilled vinegar which is 5%) that you could try 75% vinegar. Given that it's 15 times more concentrated, it should be more effective.

 

[Ratherbeflyen]

I doubt it's silicone. I bet the glass is etched and you'd have to buff it out.