Recently acquired a used tank with an unidentified white scale on the sides that I'm trying to remove. Turned the tank on it's front side and soaked the scale for a week with 100% vinegar and it still didn't scrub off. Was given advice to soak a small spot with either CLR or muriatic acid to determine if it was actually water scale, or if it was glass etching for which nothing can be done. Thankfully a small patch soaked with CLR for 2 hours has scrubbed away!...which means what I'm dealing with is probably just water scale.

So, my question is...which should I used to get the rest of this scale off...CLR or muriatic acid? I'm guessing the muriatic, because after rinsing, if the residue shows up in my filled tank water I can just adjust by using pH+ or -.

Thanks

I personally believe you are taking a risk either way. I would have to scrub quite a bit afterwards to make sure there was nothing left on the glass. The whole reason you use vinegar in the first place is it rinses away very easily and nothing is left behind to harm the fish when the tank has water in it. There have always been better things out there to remove, but there is always that lingering concern you may have made a mistake. When fish start dying in your tank (not saying this will happen to you) you'll always wonder in the back of your mind if chemical residue is doing it. I wish you luck with it. I haven't read of anyone using it,

I have the hard water stains on my 29 gal. i let it sit.. and sit.. and sit with the vinegar and it just put a slight dent in it. i tried letting it sit then using razor blades, soft pot scrubbers and such and i think i only got off what will come off. When filled you can notice it but just having the stains irritates me. YOu may have gotten off only what you could. Try filling and letting it sit a day or two to let air bubbles and such out and see if it looks any better. I got so mad with it and almost kinda f the tank if i damage it i tried sandpaper to see if it would do anything... still nothing.. so if sandpaper cant do it.. i dont think anything will.. oh it did something like swirls but not to much of else.

Muriatic acid is an archaic name for hydrochloric acid. If there are no additives other than water it should be safe for occupants after lots of rinsing. I do not know for a fact that it IS pure and I have no idea what it will do to the seals on the tank but the material itself consists of HCl and H2O and any traces left after thorough rinsing should not even have a significant effect on the pH of a multi-gallon tank.
Having said that I have not used it but someone on these forums has had to have had direct experience with using it to clean aquaria and should be able to tell us if I suggesting a path to doom.
Another way to look at this might be that if the acid is the only thing that makes the aquarium usable then try it and don't put anything expensive in it till you're sure things are unharmed.
What's CLR BTW?

I cant make any suggestions but wow I have never had hard water deposits that wouldnt come off with white vinegar and a razor blade

CLR IS Calcium Lime Rust remover you can buy almost anywhere. I have used it before, but use at your own risk I tried to keep it awy from the silicone,Put some on a rag and wipe a small area and use a razor blade and rinse=repeat until clean. I did this outside with the hose running. I hope the green folks don't get me.