Anything to prevent hard water stains?

[HooKooDooKu]

I have a glass top between the water line and the light. The bubbles from my air stone are effectively splashing water on the cover, and once it evaporates, it leaves a hard water stain. I know how I can clean it, but I'm wondering if there is anything that can be placed on the glass that might prevent the hard water stains without harming the fish (common gold and rosie red).

As an example, in another post on a similar issue someone (jokingly or not, I'm not sure) suggested using rain-x (I'm assuming that over time, that stuff would leach into the water and harm the fish, but then again I don't know what goes into rain-x).

 

[Ziggy953]

I have no idea but I don't think rain-x is a fish friendly application. You could always put some clear plastic wrap over the glass and replace it once a week or when ever it is needed.

I clean mine off with white vinegar.