Here are some of the photos of the beforehand looks. I'm not sure what type of water nor the storage conditions of the tank before I got my hands on it, but it's obvious that they didn't really care that much about it at all. The tank may look small but it's a 28 gallon euro bowfront tank made by Marineland. Sadly, the top glass part cracked in half right as I was just starting to lightly scrub it so I'll have to order another one after I get this fully cleaned. The brown stuff on the rim and slightly in the tank is when I was removing the sand (very, very fine grained) that was slightly mixed with soil of some types as I was checking to make sure that there were no leaks and it was all sealed up (which it is).
I'm not so sure on the lights or how many watts they are, will have to check when I replace them after attempting to clean the lighting fixture along with the tank later this week.
Watch out with too much rubbing!
Depends on what the hard spots are made of but if it is gritty stuff like ground up limestone, it can scratch while rubbing too hard. For the really tough stuff there is a tool made for the job. It is designed to take paint off windows and really has little chance of scratching a glass tank if done right. A paint scraper with a good new blade is very simple. The mistake some make is trying to reuse the same blade which has rusted and has pits. Those can scratch glass as they are not smooth. The second point to watch is when you get near the silicone. The blade will easily lift the silicone so watch so you don't get too close. Running parallel to the silicone helps.
Some parts it feels rough, some parts it doesn't. I haven't fully removed all of the other "gunk" from the glass or the rim at all yet, however from me rubbing on it with a light effort on the rim it seems like it just peels away, although not so much on the glass. It's more of the calcium you see built up (well in AZ that is) on the tiles if you own a pool. I haven't tried vinegar yet as I'm wanting to do this all in one go with more room, so I'll be waiting later this week to try it all out.
I'll have to try that tool (I know exactly what you are talking about) if it still feels like a rough feeling after putting vinegar on it and letting it sit for a few minutes or more.
I've had very good luck removing light calcium stains with Mr. Clean Magic Eraser -- it doesn't seem to scratch glass (unless you drag a piece of gravel with it, etc.) and doesn't appear to leave any undue residue in the tank - it particularly works well on the "just can't get them clear" areas. I've used this in the past on reef tanks and it's now my go-to on my tanks and calcium spotted glass on vivariums with misting systems.
This tank is completely empty, so I'll try that if vinegar doesn't work. I'm not sure if it'll be able to make these spots however clear, since it honestly looks like years of not fully filling a tank up or cleaning the glass whatsoever. Do you still think that it could clean it if vinegar doesn't work, or are your buildups less then what I'm left with cleaning?