Newbie - Hazed appearance to used aquarium

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Sun Bunny

Aquarium Advice Newbie
May 12, 2024
Southern California High Desert
Hello.....I am a new member, thank you for adding me. I have just purchased a used aquarium at a garage sale. It appears to be in good shape and I filled it with water as soon as I got it home to verify it doesn't leak. However, the inside glass is very hazy near bottom. The hazy section is approximately 5 inches wide and is goes around the tank (like a ring around a tub). I can't feel any difference between the clear glass above and below the haze, but it is unsightly. I contacted the seller and he said the tank sat MOSTLY empty for approximately 9 years with the water and all the decorations in the tank. (?) Now I am trying to come up with a way to clean off the haze so it doesn't obstruct the view of my new fish. Any help and suggestions would be wonderful!
Is the aquarium glass or acrylic? Glass aquariums are separate pieces of glass "glued" together with silicone sealant. Acrylic aquariums are "welded" to form a solid unit with no joints.

Can you post a photo of this haze and one of the joints?
This is a picture of the side of the tank. You can see the glass is clear at the very bottom (about 1 1/2 to 2 inches and then above the haze as well. Not sure I mentioned it, but this is a 100 gallon tank, so not easily moved. Pretty obvious it had a leak at one time...but since I will be using it as a shouldn't be a problem. Thanks for asking. It is a glass tank.
It looks like a hard water stain. This is caused when water evaporates and leaves behind a calcium deposit on the glass. Similar to limescale build up inside kettles thats common in areas with hard water supplies. This would be consistent with a 9 year old aquarium thats just been left with water in it.

Acid should clear this up and disolve the calcium deposit. Mix white vinegar 50/50 with water in a spray bottle. Lay the aquarium on its side and liberally spray the affected area and leave for 20 minutes. Then scrub with a non abrasive cloth. Repeat on all affected sides. Particularly stubborn areas may need scraping with a razor blade. Thoroughly rinse with warm water afterwards.

I have occasionally heard of particularly ingrained stains not being able to clear. This aquarium has been sat for 9 years. There are also bespoke chemical products to clear hard water stains. Ive heard of a product called Bar Keepers Friend that has treated particularly stubborn stains.
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