Mineral Deposits On Outside Of Tank?

[akainechu]

Hello, I recently acquired a used 75 gallon corner tank with three goldfish in it. Due to a time crunch, I had to set up the tank, acclimate the goldfish and put them in the tank before work, and I didn't have the time to clean off the mineral deposits that were ALL OVER the back side of the tank where their filter was. 
 
I have no idea why they let water get to the back of the tank, my only thoughts was that they were sloppy with water changes or they filled the tank too high or maybe their filter was messy, or maybe they were messy with filling the filter to prime it with water...Anyways, now I have this tank set up in my room, in the corner without much breathing room between the wall and the tank (about four-five inches between wall and tank). There are also some mineral deposits on top of the filter hood which I'm slowly working on cleaning as well, only using tank water and a toothbrush because the fish ARE in the tank. 
 
Are there any natural remedies you guys can help me with that might get rid of the harder to remove mineral deposits? I've been scrubbing with a toothbrush and tank water in a bucket, I've tried vinegar with the toothbrush and a sponge with a scrubby meant for ceramic or scratch-able pots and pans. I'm running out of ideas, and the tank has some scratches on it already from the owner using an algae scraper (horrible idea) on the inside of the tank and I don't want to add any more scratches! (So razor blades are out). I have tried using my nails to pick at the harder stuff, but sadly my nails aren't up to the job and they started breaking and cracking. Help me please!!!
 
 

 

[EllieJellyEllie]

You can take the top of the filter out, scrub it with vinegar and a tooth brush, rinse it well and stick it back in. Same with the back of the tank. Super simple, works, and shouldnt harm the fish

 

[akainechu]

The mineral deposits are too deposited for a toothbrush, I've scrubbed one small area for over an hour with no luck

 

[elmo666]

Try a Stanley knife blade. There is also a holder available that turns it into a scraper. Vinegar, as said, will help break it down, but if its been left for a long time it's going to be a tedious, lengthy job getting it off.

 

[akainechu]

Thanks so much! I actually tried using one, and it got the larger heavier deposits off without scratches, now I just need to do a few vinegar soaks once I get the time. 

 

[TrickySpot]

H2O2, hydrogen peroxide......I use it on all my fittings and fixtures at 3% concentration and it either breaks the dirt down itself, or makes scrubbing a lot easier! Don't get too much in the tank, not sure of the exact concentration fish can handle, but I personally am very generous and no fish have moaned!
 
Otherwise, I have a spray bottle with vinegar.....for day to day water deposit stains.