I would suggest first using Diet Coke to shift the stains, you need to let it sit on the surface rather than just wiping on, needs a good steeping so you’ll need to create a dam around the area you want to treat, make sure you use the caffeinated version and not caffeine free because you want the chelation ability of caffeine to mop up any dislodged compounds that may recombine with the surface you are trying to clean. If this doesn’t work then try repeating again but adding Sodium Bicarbonate and mixing on the surface, the reaction will become more Alkiline and this may be needed instead of Acid pH.
Obviously you have experimented using stronger Hydrochloric acid so I would like to point out that since the talk has evolved to possible Silicate deposition under no circumstances should you try to source or use Hydrofluoric acid to do the Job, no tank stain is worth a life, just don’t go there.
Piranha solution though is used to treat Archaeological glass to clear staining (
https://www.sciencedirect.com/science/article/abs/pii/S1296207412000593) but I wouldn’t recommend that either even as a weak solution because If it ends up somewhere you don’t want it will eat organic compounds quite vigorously generating a lot of heat and irreversible destruction.
A safer method for removing silicate deposits (still hazardous) would be using Sodium Hydroxide in conjunction with Sodium EDTA, the need to mix the hydroxide with a chelate was pointed out above as to reduce the possibility of recombinative chemistry back onto the glass surface being cleaned. Here’s a paper discussing this (
Improved Methods for Removal of Silicate Deposits) but note the substrate to be cleaned is Carbon Steel and not Glass, however if you note from the abstract of the Archaeological glass cleaning link that Sodium Hydroxide was deemed too aggressive on some surfaces (not sure what type surface you would classify aquarium glass certainly not something from antiquity that needs to be handled like it will turn to dust if you look at it the wrong way), they did use EDTA as a chelate though.
Sometimes it’s just easier to get a new tank or live with what you’ve got!
