Salt spray and creep can become permanently attached to the glass surface of your saltwater aquarium. Unfortunately, the deposits are not just salt (sodium chloride) that is easily washed ways. The minerals in saltwater can form a very difficult substance to remove from the glass when allowed to build up. While you may have ignored this for a holding tank, it can become an issue when you want to move that tank to an area where it will be viewed. Now you have to face the challenge of removing the minerals from the glass.
You might have tried some ineffective methods. Simply scrubbing at the white substance with fresh water will look great until the glass dries and you see that the buildup is still there. Sanding the glass with fine grit, wet or dry sandpaper also will not do the trick.
Various solutions such as vinegar, ammonia, calcium/lime/rust (CLM) remover, or muratic acid may not be effective. In addition, muratic acid can be downright dangerous. Just getting a whiff of the fumes can cause serious damage to your lungs.
Vinegar or CLM
You can use vinegar or CLM to remove the salt creep, but the important factors are applying the treatment long enough and using enough elbow grease.
Keeping the glass immersed in either vinegar or CLM over a period of time will dissolve the mineral deposits. Since the vinegar and CLM evaporate fairly quickly, you need a method of keeping the glass wet with the solvents.
Put a paper towel soaked with the solvent on the glass, sealing it with a layer of plastic (such as a 12-inch long, 4-millimeter thick bag) and let it soak overnight. This will help with many deposits, but you may need even longer treatment with those with a thick deposit.
It can be easier to treat a disassembled tank because you have only flat pieces to work with. If you are rebuilding a tank and want to remove the minerals from all of the panes, just layer them on a flat surface with vinegar in between them. Leave overnight or as long as it takes, then scrape the minerals off with a single-edged razor blade. You may find that you have to dampen the glass surface and scrape with the razor blade a few times to get the glass completely clean. Clean the bonding surfaces with acetone and reassemble with silicone caulking.
If you want to clean up a functioning tank, you can use the same method on the outside of your tank by simply taping the solvent/paper towel/plastic assembly to the upright glass with duct tape.
Distilled vinegar works just as well or better than the CLR and was less caustic to the skin. Vinegar is far cheaper than CLR. It may take a while to dissolve the minerals, but you can find many other uses for the leftover vinegar around the home. Not only is it useful for cleaning many surfaces, you can, of course, use it for making salad dressing.