The problem with having glass shower doors is that the only way to avoid getting built up water spots is to use a squeegee after each use. Now getting your 9 year old to get motivated to do this is a different story. So the reality is you need to find the best cleaner for shower doors.
Most areas in this country have mineral laced water, some worse than others. So, avoiding water spots is really difficult on clear glass. Overtime this just continues to build up and get more and more difficult to remove.
There are so many cheap products on the market that claim they can clean your shower glass and remove this buildup. So can remove a dusting of minerals, however if you really have a problem with mineral buildup on your glass, faucets and fixtures, you need a specialty product.
I know you have seen videos of do it yourself vinegar and water mixes that can take care of this problem, or spray on products that claim you can apply and wipe off. That is simply not true.
Here is the product and the solution to this problem. It is called the Bring It On Cleaner. This product has a jewelers grade abrasive that is gritty enough to cut through hard minerals, however delicate enough to not scratch you glass surface.You can also get a protective sealant that you spray on after the glass is clean. This will allow the water to sheet off the glass for up to a month.
Now this is how you clean your shower door. Here is a review done on the Bring It On Cleaner by a popular blogger, Mr Garbage Disposal
Now remember the next time you are looking to clean your shower door and remove mineral buildup, get the product that actually works.