has anyone heard of or done this before? the idea JUST popped into my head.
i believe it would be safe for the fish, since i'd only etch the outside, the back mainly.
I do stained glass, which sometimes includes using an etching solution.
I'd think if you used the solution to do it--and not "actual" etching (ie carving into the glass)--it shouldn't effect the sturdiness of the glass. It's more of a chemical reaction between the things you apply than really taking away from the glass.
you know you use acids to eat a design into the surface of the glass right? i think it would affect the strength of the glass. it may not be much of a problem with stained glass, but with all the pressure exerted by the water, i think youd be tempting fate.
there is stuff you can use that you paint on. it is removeable and it has a frosting medium you can add to the stuff to make the colors opaque. there is also a clear color. i used it on a window i had in a bathroom (it was in my shower so i couldnt hang blinds or curtains)
I'd guess it would depend on how extensive you're looking to do. Frosting the whole thing... maybe so... but just a design?... ... I'd doubt it, and doubt it even more for smaller aquariums.
I can't imagine it'd be any worse than a scratch.
(Now... ...don't get me wrong, I could be mistaken. But I... can't imagine it being that bad.) (And I don't think I'd do it, because I might get bored. It'd be like a tattoo... something I'd have to not get bored with, and I get bored easily.)