Cleaning lime deposits

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Aquarium Advice Newbie
Nov 3, 2023
I've inherited five acrylic fish tanks. I think they're all 50 to 75 gallon capacity. All are heavily coated with a hard white substance ("scale") which I understand to be a calcium deposit left by chemicals suspended in the water.

I looked for advice on removing this stuff. All the recommendations I found say the same thing: get a commercial tank cleaner (I tried API Safe & Easy) or white vinegar. Spray or wipe the substance on the tank, wait a few minutes, and wipe it off.

Those things didn't do squat. I turned one tank on its side, put a paper towel over an area that included heavy deposits, poured vinegar on it, covered it with plastic film to prevent it from evaporating, and left it overnight. When I wiped it off the next day, the lightly soiled parts appeared perfectly clean; the heavily soiled parts seemed little better than they had been, perhaps no better at all.

What now? Is the water in my area (Sacramento) different from the water everywhere else, so that the solutions that work for everyone else won't work for me? Am I just out of luck?

I'm thinking about trying phosphoric acid. I've had good results removing lime deposits with it before, but I've never used it on acrylic plastic. The reference site I checked said that it should be safe unless I use a high concentration and left it in place for several days.
I use lemon juice on glass and I believe it's also safe for acrylic. ( test a small area in the back of the tank before going crazy with the whole tank. ;) (y)
I tried applying lemon juice with my 24-hour no-evaporation procedure. I think it was more effective than vinegar, but still not very good -- after two applications the heaviest deposits were still visible. I'm going to see what phosphoric acid will do.
A couple of more notes.

First, I discovered that Easy Off makes several cleaning products, some of which would probably be useless for tank cleaning. Be sure to get the oven cleaner.

Second, Easy Off oven cleaner is available in a pump-spray bottle, which is much cheaper per ounce than the pressurized spray can, and probably is less harmful for the environment. I've never seen this in a store, but it's advertised on the Web.
And a final note on the notes.

I discovered that the pump-spray configuration is actually a different product, Easy Off Oven and Grill cleaner. The product description says something to the effect of "suitable for use on hot grills." That made my suspicious nature perk up, so I asked in a Q&A section whether that meant it was suitable for use only on hot surfaces. The answer I got was: no, it works just fine hot or cold.

I repeat, this is a distinct product and I haven't tried it, but it sounds comparable to what I'm using, and a lot more economical.
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