Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Water spots are often because of the minerals in the water. If the water did not splash...
Inside the tank, above the water line: Keep the water level up. If the minerals are still visible, then drop the water level enough to clean with vinegar.
On the outside of the tank, or on the plastic rim: Wipe it before it dries. If it has recently dried wipe it with a rag dipped in vinegar. A drip or two of vinegar landing in the tank is not a problem
On a glass lid: Wipe while it is still damp. If it has dried but is not much, then a vinegar wipe might be enough, though if there is a lot of cleaning to do I prefer to take a glass lid into the shower and hose it off. That way, too, I can get some of the crud out from the hinge, too, without worrying about it landing in the tank.
On any of these surfaces, if the deposits are older, or the minerals have built up too much you might need much stronger acid and more cleaning. Perhaps a razor blade.
Acrylic: Only use approved materials. Acrylic scratches a lot more easily than glass.